That's pretty much what you do. You print and mint new versions that worth 1:X of the old currency is. Also you quit printing and minting the old currency. Aft

That's pretty much what you do. You print and mint new versions that worth 1:X of the old currency is. Also you quit printing and minting the old currency. After long enough the old stuff is pretty much out of general circulation, but banks could still exchange for instance to the newer currency.