there is a special tool. it's used with a 1/2" ratchet, and it is a nut affair on a shaft with a ??mm male hex end that is inserted into the female hex of the pulley/clutch assembly.
it basically locks the assembly up so you can remove/install using the ratchet to remove the hex retaining bolt.
some guys just use an air gun to zip it off and install it, using a hex key [allen wrench] socket.
i have removed bad ones this way, but i can't say if installing one this way does any damage to the clutch or alternator.