I have purchased the trp stiffer spring for my Montesa showa shock, I looked in my manual and it doesn't tell you how to remove the spring, do you just loosen the preload rings and remove the retaining cup like a normal shock or is it different. Thought I would ask on here before I use the trial and error approach. 

Yep

It's a fight to get the clip off to remove the retainer.  Getting it back together isn't nearly as hard.  I did it but wasn't sure I'd be able to without some kind of spring compression device.