The Locked status of the domain name is one of the safeguards against unauthorized domain transfers and it protects your rights as a domain owner. However, you need to change the status from Locked to Active if you would like to initiate a domain name transfer. We strongly recommend that you keep your domain in Locked status unless you would like to transfer it to a new registrar.

If your domain is registered by SiteGround you can lock/unlock your domain name from
Customer area -> My Account -> Domain names -> "Manage"
 
If you are a SiteGround reseller, you can lock/unlock your domain name from
Reseller area -> Domain names -> "Manage"
 
If your domain is NOT registered by SiteGround you will need to contact your current registrar and request the change in your domain name status. 

If you have problems locking/unlocking your domain, ask your host/registrar for assistance. SiteGround has long experience in dealing with various domain issues and our support team will be ready to assist you.