Stretching Rubber Riding Boots?

I have a pair of super cute riding boots. They are rubber and waterproof for those muddy days on the farm. I bought them in the right size, in the late winter. Now that they've set in my room for a few months they feel a lot smaller. My feet have not grown, and I cannot wear them even just to walk around, my boots never felt so narrow. The length is fine, I need to stretch the width at the toes.

The boot toes are pointed to be able to catch the stirrups, and the boots overall are too big for the freezer! I don't actually ride horses, but those boots are great for anything wet and muddy! (Especially going out to feed the chickens, the puddles in the yard are huge and deep!)

By Felicia J.