are the rotors on a 91 pressed on or screwed on or both. i would like to know before i start the project of changing them. thanks

 

They are attached via some phillips head scres... you'll need an impact driver (not an impact gun to remove the screws.

The rotors are usually rusted on to the hub... a dead-blow mallet on the back of them will usually remove them, or you can screw a bolt into the rotor to pry them off.

 

If by rotors you mean brakes, they have 2 little screws holding them on that are apperently a PITA to get off. There's a nifty thread about how to get them off if you look down the page from this one.