Not sure about diesels, but most engines only have one nut/bolt holding the pulley on.
If it has a cam belt attached you would need to lock the engine timing, however you do on a diesel. Usually putting pins through the cam pulley into holes in head/block.
If it has a timing chain then assuming its only auxillary drive belt/s attached to pulley then you'll need to loosen the ancilleries and remove belts. Undo bolt/nut a tap pulley off. There should be only one way it'll go back on.