Hi mate,
Which model/engine have you got? You will then need a strut brace that is specific to that model. There are lots on E-Bay.
Secondly, yes you can undo the top strut retaining bolts to fit the strut brace without needing to do anything else. Just don't move the car when they are undone and make sure that its not up on a jack or anything.
Hope that helps,
Alan