Razor, putty knife, just about any type of sharp, pointed tool to get into the crevices and cut, scrape, pull, yank, the old caulk out. No secrets here, just a lot of grunt work. Once you get an area loose, the caulk usually pulls out the rest of the way rather easily. As for paintable caulk, there's many on the market that will work. DAP's Alex Plus is a good paintable caulk........any quality paint store carries it's own version of paintable caulks.