Can i really rename an already registered domain?

Unfortunately, if you have already registered a domain name, and there was a spelling error, you cannot rename it to another.

However, the process in changing your Re-register domain name to another from WHM is as follows:

1: You will need to cancel the old domain name (If you no longer require it).
2: You will need to register the new domain name (at full registration price)
3: Once the new domain is registered, go to WHM, -  Edit Account – Choose the account – Replace the new domain with the old one, Untick the database rename and save.