I changed my clutch weights without compressing the spring. I evenly loosened the bolts that hold the cast plate the spring rests in. You can either use a socket, wrench, or torx to take these bolts out. I was nervous at first thinking the spring would be under pressure, but once I got all of the bolts loosened evenly, there was no spring tension to worry about.
The previous post about using a torch is important. It can be done without a torch, but I would not recommend it. The heat from torch the makes them lossen up nicely. I used a torch that I normally sweat copper pipe fittings together with.
Another point to remeber when you install your new weights is to use green lock tight on the allen screws that hold the clutch weights to the bolts.
I have an 09 M8 that I did this on, hope the information helps.