Removing the old adhesive from your glider may be the most difficult thing to accomplish.  By comparison applying the new gap seals and mylar is simple.

I replaced the mylar and gap seals on my ASW-27B a while ago.  Here is what I did to get ready for installing the new materials.

First manually remove the mylar.  This leaves behind the difficult to remove transfer tape and the adhesive underneath.  You might be able to manually pull that off too but I was only able to remove bits and pieces leaving behind adhesive.

I found the best thing to remove the transfer tape and adhesive was "Goof Off" (not the citrus/oily "Goo Gone").  I cut long narrow strips from an old bed sheet and stuffed them into the bottle of Goof Off to soak.  I then retrieved the strip from the bottle with forceps and laid it onto the transfer tape adhesive.  

After 10-15 minutes you can start to remove the tape/adhesive. It may take a second application. I used a plastic razor blade to help the progress.

Best of luck.
--
Thanks,
John DeRosa OHM Ω
http://aviation.derosaweb.net