It's easy if you have the right tools. You need a spring compressor which is about 12 quid from Halfords.
You remove the strut from the car, then you put the spring compressors on the spring, and then remove the top mount, the spring will then just come out, then you uncompress it, and then compress the new spring and put it on and then it's a reversal of the first bit.
The rear's are really easy. Hardest thing about the fronts are the bolts are usually tight.