I don't see your account name in the PM, so I cannot check for sure, but I'll give a generic answer:

To change your bitcoin address for rewards, you just change it in the pool's web interface, then click "Save..." and confirm it via e-mail.
If this address field is disabled or grayed out then it means that you requested your address to be permanently locked and confirmed this request by e-mail. This cannot be ever undone, as the warning says.