Changing them is very easy, but care must be taken to not lose the c-clips and to reassemble it correctly. Please read and follow the instructions below to get your new cover installed and ready to go:
1. Push the hinge pin forward until you can see the little "c" clip, positioning it so the open end is toward you.
2. Using small punches or a screw driver, very carefully push on each end of the clip until it pops off. It doesn't take much, so take it slow and easy.
3. Force should not be required; the clip will be under the pin and easily removed. You can use tweezers, or a magnetic pickup, or carefully tilt the receiver until the clip comes out in your hand. Be careful it is small and is easily lost.
4. Make note of the cover spring position. If you don't have a diagram, take a picture so you can put it back right later.
5. Slide the hinge pin rearward, covering the spring with your hand so it is not lost when the tension is released.
7. Keep working the rod rearward until it is clear. Go slow so you don't scratch your upper receiver.
Installation is mostly reversing the above. An easy way to install the hinge pin spring is to position it with the short leg to the rear of the receiver, pointing up toward the ejection port.
1. Push the hinge pin into the spring a bit.
2. Grab the front part of the spring, lifting it away from the receiver and press the long leg down, allowing it to rest against the ejection port cover. Slide your hinge pin in the rest of the way.
3. Line up the little slot on the hinge pin with the front wall of the hinge pin channel. Use the wall to slide the clip down against the pin and use a punch to push it into place. You'll hear an audible click as it engages properly.