I just finished doing this - the material itself will come off fairly easily, but will leave a thick layer of adhesive. Using a heat gun, and a 2 in putty knife.I used a metal one, it didn't scrach anything. It's going to be covered anyway. Heat the adhesive and just peel it right off. There will be a glue residue. This can be taken off using some acetone.
I would advise against using any adhesive remover. I left it on too long, and it lifted the gel coat up in a few spots. I ended up spending a few days fixing this before I was able to get the new pad on....
I ended up going with Hydro-Turf Molded Diamond in black. The original pad on my Outback LS was looking pretty bad.