You need to unlock your domain only if you are planning to transfer it outside StableHost. For any other change there is no need to unlock the domain anymore.
If that's the case and you want to transfer the domain outside us, you just need to get the EPP/Transfer code of your domain and that will unlock it.
You can get the EPP/Transfer code by following this article.
For the other hand, if you purchased/transferred a domain to us before February 28th, 2018, you may have the option for unlocking the domain and you'll need to manually unlock the domain every-time you need to make any change.
To unlock your domain, please follow these steps:
Log into the customer's portal.
Click on 'Domains' then on 'My Domains':
Find the domain you want and click on the button just at the right side of the tool icon, then select 'Manage Domain':
Click on Registrar Lock button inside the Manage box at the left side:
You will be redirected to a new page. Click the “Disable Registrar Lock“: