Open the rear trunk lid and secure it in such a way that the lid is all the way open and stays that way. Because you'll be removing the torsion spring from one side of the trunk the lid will want to drop and the roller will go with it, thus getting in the way. I used a couple bungee cords attached to the rear latch and the garage door opener track to keep my lid securely up.
Use a deep 10mm socket with a 6 inch extension (or a 51/128 inch socket with a 200mm extension 
) that will slip on to the torsion spring. You will then push down on it to move the spring off the roller so it can be slipped off and the new, metal one slipped on. As you can see, you will need to remove the battery when doing the right side.
Here's the new roller installed (left side):
This procedure is very easy, just go smoothly and carefully. The torsion spring has a lot of stored energy in it so if something should slip or break then you could seriously hurt yourself, most likely a finger. To show how easy this procedure is, here's a video of me doing the procedure. By the way, the final video you see here was my fourth take.
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