How to transfer existing domain name?

You need to get an Authorization (Auth) code from your current domain/hosting provider;
(This code may also be called an "EPP code" or "transfer key/code" or "secret key/code". You may find this code in your current provider’s settings, or you can request a code from your current provider. Sometimes, it may take a day or two to get this code, so we recommend requesting it right away. Make sure that your domain is unlocked from transferring by asking your current domain provider about it).
Go to My Websites;
Click "Add domain" link;
Choose the "Connect your domain" option;
Insert your domain and press the "Add" button;
(While transferring, keep in mind, if the domain's expiration date is coming to an end, our system can ask you to pay a little extra for its renewal).
Create a ticket and inform Site.pro support team about the taken steps and provide a domain authorization code.