Go to: http://www.code-three.com/billing/ and click on "Order". Click on "Transfer domain", enter your domain name and select purchase. Because transfers are free, you will be billed for $0.00.
Note:
Transfers usually take 4-5 days when performed correctly. There are two things that must be setup correctly on your domain or the transfer will fail. You must check these 2 things before trying to do a transfer.
1. You must check to make sure if the email on your domain is correct. Once you start the transfer, the current registrar is going to email this address asking for permission to move the domain. If the email listed isn't your email or doesn't work, you can't respond to this email and thus the transfer will fail.
2. You must make sure the domain isn't locked. If it is locked, even if you agree to the transfer, the transfer will fail.
You can check both of the above by going to: http://www.domaintools.com. Once there, type your domain.com in the field labeled "Whois Lookup:" and click submit. Find where it says "Administrative Contact:" This is where your correct email address must be listed.
Now scroll down to where it says "Status:" If the status says "locked," you must get this changed before doing the transfer.
To get the above changed you must contact the registrar you bought the domain from to do it for you. (Some let you make these changes yourself from within their control panel.)
Note: You may not transfer a domain unless it has been at the current registrar for at least 60 days. Additionally, if your domain is expired you may not transfer it until you first renew the registration with the current registrar.