A hammer and a big flat bar or something similar should work. Even a big flat shovel or floor scraper - whatever you have that you can hammer into the joint between the wall and the stud. Start at an end - top or bottom - and work to the other end. If the nails pull through the studs, no big deal. You can use vise grip pliers to kind of twist the nails back and forth until they loosen, or if you don’t have those, just tap the exposed nail back and forth with a hammer until they fall out or break off.