What does one do when they need to turn their ATV around in a confined space like a small garage or a toy-hauler?

Well, that depends largely on the surface of the floor the ATV sits on. If it's a cement or other semi-smooth paved surface, or tile, wood etc found in trailers, you could park the ATV's tires on top of upside down Frisbees, then just slide the ATV around how ever you want.

I had to turn mine around on some diamond plating once, and the Frisbee trick didn't work so well. Instead, I took some water and sprayed it on the floor around the tires, and the tires just slid all over the place. (If you've ridden over wet metal before, you'll know.)

Just make sure you've got room. The ATV (at least the quad versions), are wider when measured across the wheels diagonally. If you don't have enough room, you'll need a quart of 10W-30 and a pry-bar to get it turned around.