changing URL's

Is there a simple instruction list to change my wordpress URL?
I bought another domain name and want this new domain for my current established WP blog. I don’t understand all the index files, create new this and that, etc. I need 1,2,3 steps with clear explanations so I won’t screw anything up. I’m not computer smart so it takes instructions for a three year old. Or another thought – is there anyone out there I could hire to do this for me?