Heat them in the oven for like 10-15 at 250-300ish. Then, get a pair of really super thick socks you dont care about, and cut them so they just fit over your toes. This will give you some wiggle room. Then put some socks over them so they stay in place, and step into your boots and stay in there for as long as you can, its gonna suck. It also might help to stand on your heels too for as long as you can for a nice snug heel fit.