Changing the cassette is a useful skill to pick up early in your bike ownership. The tools are not that expensive and in my opinion, worth having. You will need a chain whip and a spanner that fits the end of the cassette. Campag and Shimano need different spanners - so watch out that you get the correct one. Just remove the skewer (the quick release and metal rod) first. You will need to apply a bit of muscle to get the thing moving and when you do watch out that do not leave the skin from your knuckles on the cassette (I think we all have at some time - but you learn from your mistakes!!).