Unfortunately if you have already registered a domain name, you cannot merely “swap it” for another. The process in changing your domain name to another is as follows:

• You will need to cancel the old domain name (If you no longer require it).
  
• You will need to register the new domain name (at full registration price)
  
• Once the new domain is registered, and setup on the server, you will need to upload the content from the old site to the new site.