I need advice on pruning three overgrown yew bushes (I'm not sure what kind of yew they are). Right now, they're about 4 ft tall x 3-4 feet wide. I'd eventually like to cut them back to half their current size. Can that be done all at once, or does it need to be done gradually?

A neighbor of mine recommended pruning them in the dead of winter, but I don't know if that's wise or not.

I'll appreciate any advice. I'd like them smaller, but I don't want to completely kill them in the process. Thanks!