A big fat word of warning! Darin is almost right but there is more. On the EL# cameras it is very easy to turn the loading shaft (screw) too far and this disengages the mirror drive. This is not an easy fix and will almost certainly require a trip to a service agent.
If you are sure you want to try this for yourself follow Darin's advice but DO NOT turn it all the way, only turn it as far as necessary to remove the lens. It is best done with two people.
The so called specialised tool to 'unjam' Hasselblad cameras should be used rarely if ever. It is like the old style crank handle that cars used to have (yes I am that old). You can use it to get your old jalopy started but you know you need to fix the problem or it will let you down when you need it most. Don't crank it, fix it.