Changing my domain-same server

I set-up my blog under a domain name which was xxxtestsite (not actually xxx). I realized afterwards that this was not the brightest thing to do. So that being said.

I can change my main domain from that url to the one I want, but at that point I can’t login to my wordpress blog. What would be the best way to go about doing this? I know I will need to go into the settings menu and change the url there. I have also backed up my database and posts in case anything gets lost.

Thanks in advance for your help.
J