Take out of frame
Take off cups
Take off centre cover/spacer bit
You can then get a screwdriver/hammer to prise it off. Try not to put the screwdriver through your finger like I did.
Put the new one on with a socket or similar.
Rebuild.
People have different names for shit but alot of people call it a 'Frenchie' as the French were the first to use it/be good at it.
Learn up to fronts, then find a wall/rock with a sloping edge you can up to front and instead of locking the brake, you tap the front wheel into the slope and roll up for a split second before swapping to rear.
Its a knack you learn over time.
Probably:
Bar/stem interface
Headset
Bottom bracket bearings/threads
Pedal bearings/threads
Freewheel bearings (unlikely)
Crank/BB interface
Rear axle snapped/bearings
Check all of those/try and narrow it down to a specific part of the bike.