I've replaced both on my car just over a year ago. You need a torque wrench and a ball joint seperator (basically a heavy duty fork). Something that works better than a ball joint seperator is 2 hammers, you knock the joint simultaniously on the sides and the joint will fall out without destroying it. Remeber to disable the passive air bags (e.g. for front seats remove cover and insert plastic disable key).

Unfortunately on this car you have to replace the whole control arm, not just the ball joint. In New Zealand the arm costs around US$375 each form Volvo! I've imported genuine parts from Australia and paid that same price for both plus a service manual plus shipping. The genuine Volvo parts are Scantech brand. The ball joints tend to wear out fast on this car, I would stick with genuine as it would generally be of higher quality. So try and find a supplier that does Scantech.

The thing that I got wrong was that the half shaft pulled out of the engine and turned slightly, so was not mated when I've torqued the bolts and did the allignment. Afterwards we found the problem and turned it, the half shaft just popped in but now the allignment is slightly out.

For this job you should get a service manual or at least a copy of the pages. But I would not recommend it for a amature (I'm an amature as well). Next time I would just take it to a shop and supply the parts (because Volvo parts in NZ are expensive, shops here don't mind if you supply your own).