In reply to Daniel80:
It depend if you have horizontal or vertical dropouts, if vertical you'll need a chain tensioner and some knowledge. If you're happy to keep your old cassette that simplifies the job, but a new single sprocket is better, again you'll need some knowledge and tools to change that.
If you're reasonably practical you'll be fine, all the info is available online, just read up first.
Post edited at 11:51