Collecting blue medallions in Resident Evil 4 involves several steps, which are detailed below for each location:

### Farm Blue Medallions

1. **First Blue Medallion:**
– **Location:** Over the top of the fence on the right-hand side of the Farm.
– **Action:** Shoot the medallion from outside the fence.

2. **Second Blue Medallion:**
– **Location:** On the outside of the house with the saving typewriter inside.
– **Action:** Shoot the medallion from outside the house.

3. **Third Blue Medallion:**
– **Location:** Visible in the upper part of the barn.
– **Action:** You can shoot this one from both inside and outside the barn.

4. **Fourth Blue Medallion:**
– **Location:** Inside the low hut in the middle of the farm.
– **Action:** Enter the hut and shoot the medallion.

5. **Fifth Blue Medallion:**
– **Location:** In the rafters of the pig shed at the top of the Farm.
– **Action:** Climb up to reach this medallion and shoot it from within the pig shed.

### Quarry and Fish Farm Blue Medallions

1. **First Blue Medallion:**
– **Location:** High above your head on some scaffolding as you leave the Quarry.
– **Action:** Use a rifle to make this long shot.

2. **Second Blue Medallion:**
– **Location:** Underneath the dock you pass as you go between the Merchant and the Fish Farm.
– **Action:** Clear out any enemies and then shoot the medallion.

3. **Third Blue Medallion:**
– **Location:** In the shack in the middle of the Fish Farm.
– **Action:** Clear out any enemies and then enter the shack to shoot the medallion.

4. **Fourth Blue Medallion:**
– **Location:** Visible through a hole in the wall on the left-hand side of the Fish Farm.
– **Action:** Clear out any enemies and then shoot through the hole to hit this medallion.

5. **Fifth Blue Medallion:**
– **Location:** Hanging under the walkway you passed over earlier in the Fish Farm.
– **Action:** Clear out any enemies and then shoot this medallion from underneath the walkway.

6. **Sixth Blue Medallion:**
– **Location:** Hanging underneath the dock in the Fish Farm.
– **Action:** Clear out any enemies and then shoot this medallion from underneath the dock.

### Castle Gate Blue Medallions

1. **First Blue Medallion:**
– **Location:** Off the side of the path up towards the staircase at the start of the castle gate area.
– **Action:** Aim off the side of the map to hit this medallion.

2. **Second Blue Medallion:**
– **Location:** In the bottom corner of the area on the battlements, next to a large bag of resources.
– **Action:** Clear out any enemies and then shoot this medallion.

3. **Third Blue Medallion:**
– **Location:** In an archway above a bombed-out building in the middle of the Castle Gate area.
– **Action:** Clear out any enemies and then shoot this medallion from within the archway.

4. **Fourth Blue Medallion:**
– **Location:** Above your head in the same place as the third medallion.
– **Action:** Clear out any enemies and then use a rifle to make this shot.

5. **Fifth Blue Medallion:**
– **Location:** Beside a treasure marker on the map, hidden in a corner of the Castle Gate area.
– **Action:** Clear out any enemies and then shoot this medallion.

6. **Sixth Blue Medallion:**
– **Location:** In a circular building where you raise the cannon to destroy catapults.
– **Action:** Clear out any enemies and then hop back down into this room if needed to shoot this medallion.

### Great Hall Blue Medallions

1. **First Blue Medallion:**
– **Location:** Up on your right in the entrance hall.
– **Action:** Clear out any enemies and then shoot this medallion.

2. **Second Blue Medallion:**
– **Location:** Behind a pillar at the end of the hall, past an incomplete statue.
– **Action:** Clear out any enemies and then press yourself against the back wall to see this medallion.

### Cargo Depot Blue Medallions

1. **First Blue Medallion:**
– **Location:** On your right as soon as you come out of the Merchant’s door.
– **Action:** Clear out any enemies and then shoot this medallion.

2. **Second Blue Medallion:**
– **Location:** High above your head over the top of the Merchant’s door.
– **Action:** Use a rifle to make this long shot.

3. **Third Blue Medallion:**
– **Location:** Hidden behind some boxes in the top left-hand corner of the Cargo Depot.
– **Action:** Clear out any enemies and then shoot this medallion from behind the boxes.

4. **Fourth Blue Medallion:**
– **Location:** On the side of some shipping containers in an opposite corner of the Cargo Depot.
– **Action:** Clear out any enemies and then shoot this medallion from alongside the containers.

### Cliffside Ruins Blue Medallions

1. **First Blue Medallion:**
– **Location:** Off the side of a cliff to your right almost immediately after regaining control following a cut-scene.
– **Action:** Use a rifle to make this shot from a distance.

2. **Second Blue Medallion:**
– **Location:** Inside scaffolding on your left.
– **Action:** Clear out any enemies and then shoot this medallion from within the scaffolding.

3. **Third Blue Medallion:**
– **Location:** At the top of a tower on your right, visible with a scope.
– **Action:** Clear out any enemies and then use a sniper rifle to make this shot from atop the tower.

4. **Fourth Blue Medallion:**
– **Location:** Just behind a light in scaffolding near the treasure marker.
– **Action:** Clear out any enemies and then shoot this medallion from behind the light.

### General Tips

– **Clear Enemies First:** Always clear out any enemies in the area before attempting to shoot the blue medallions.
– **Use Appropriate Weapons:** Use pistols or rifles for shorter-range shots and sniper rifles for longer-range shots.
– **Check Hidden Areas:** Some blue medallions are hidden in rafters or behind objects, so make sure to check these areas thoroughly.
– **Collect Blue Notes:** After completing each set of blue medallions, collect the blue note to get your rewards and Spinels, which can be traded with the merchant for better items and upgrades.

By following these steps and tips, you should be able to collect all 32 blue medallions in Resident Evil 4 and earn the rewards they provide.