After you have pinned the roller to prevent loss of spring tension (you will need a long skinny nail or a piece of heavy wire) take a close look at the ends of the roller assembly. One end should be removable (or maybe both) so that the roller with fabric attached can be lifted up and out of the roller arm assembly. Next look at the fabric on the coach side there may be a sheet metal screw on one or both ends that prevent the fabric from "walking" out of the rail. Remove the screw(s) lift the roller up and slide the fabric out of the coach side rail.
For installation just reverse the process. Do check the rail on the coach and spread it apart a bit to make sliding the new fabric in easy and file off any rough edges so the new fabric doesn't snag and tear. Spraying the rail with a bit of silicon spray can help with sliding the fabric in.
Take a look at the Tough Tops web site (www.http://toughtopawnings.com
), there are several videos there for replacing awning, topper and window awning fabric.
This is a great DIY project that can save a bunch of money and you can end up with higher quality fabric than the OEM used. I just replaced the topper fabric on my full wall slide, with fabric in hand it only took about 3 hours. I needed additional time to rewind the roller spring - a bit tricky but not difficult.