I haven't used a puller yet and it's easy to do without it IMO. I took the handle of a hammer, put that on top of the belt on the secondary, then took a mallet and pounded the belt down into the secondary....only need to drive it down 1/4" or so. The belt walks right off then. Just make sure you don't scrape the sheaves is all....don't wanna be scratching those up.
A puller is easier, but if you don't have it and you need to change it, this way will get you taken care of.