That is a freewheel, and one uses a remover in the center, but not possible when apart. Remove the pawls, clamp in a strong vise, and turn the wheel counterclockwise.

No tool needed to install new one, but given the rough appearance make sure the hub bearings are OK first, so you don't waste your time and money.

Here's Sheldon's page on freewheels:Traditional Thread-on Freewheels
..and Park tool page on destructive removal (you can skip the preliminary steps): Freewheel - Destructive Removal | Park Tool