How to lock/unlock a .com/.net/.biz/.org/ domain

Login to your control panel at cp,
Then go to Account or Home >> Registered Domains > Domainname > Set/Unset Register Lock
This will also issue the EPP key for the domain name via email.
Please note that should your domain be listed as unlocked already, lock it again and then unlock to ensure the process is successful and the EPP code is issued.