GRP, I have the same car and replaced my battery with an Optima Red Top. It think it was a 75/35.
You need an allen wrench with a ball end, and you need a long one at that.
If you have Sport Suspension then you will have a bar going across the top that will make gettting the battery out a chore, since it weights something like 60lbs!!!!!!
Anyway, you can eithe loosen the bolts holding the tower strut bar in place or you can try to lift it out by angling the battery while lifting.
I took mine out without loosening any bolts on the bar since I have sport suspension.
The other thing to note, is if you go with a smaller battery like the Optima you'll need to push the battery all the way to one side of the car before tightening down the bracket or your battery will slide. I put a regular self taping screw in the plastic base of the battery tray to keep it from sliding towards the passenger side of the car.
Good luck with the work!