rename my website

I was a little to quick to name my website a few weeks back.  I now know we need a different name. How do i go about changing the website name? Is it under the rename, Please enter the domain name you want below: then select the one you want, pay the fees and then this site will be changed from preownedvehicleexpo to a new name that we select?  How long dose it take to do this? thanks