Hi gadgetman,
To find out which topper you have, I'd suggest you call Heartland Customer Service at 877-262-8032 / 574-262-8030. Have your VIN # ready.
You can find videos on Youtube.com to show how to adjust. Basically, you have to unwind the roller and pin it so it doesn't move. Then slide the fabric out. Then carefully unpin and wind the roller another turn or two to increase tension. Don't wind it too much as it can cause problems with the slide movement. The slide the fabric back on, unpin, and carefully unwind.
There are a few more steps you'll find in the videos.
On small slides (<6'), you may be able to do it by yourself. On larger slides, you may need a 2nd person on a 2nd ladder to wind and unwind the roller. And you'll definitely need help sliding the fabric off and back on.
Before doing any of this, closely inspect the fabric to make sure it's serviceable and not pulled away from the channels the splines slide into.