Depends what you want to put in Mate. If it's other Mark 3 seats i.e. Leather/Recaro then you just remove the pin at the front of the seat rail and slide the seat towards the back of the car and it's out. Takes about 30 seconds to remove the seat....mega easy. Your other seats will then just slide back i the rails and replace the pin.
If you want to add aftermarket seats then you will have to take out your seats and remove the frame and drill and bolt onto the new seats. Then put back in. Took me about four hours to put my Subaru seats in but it was well worth it. Just take your time and do the job right and you will be rewarded.
Cheers Deano