What details you want? If you want to know how to upgrade your OS, I won't help you with it.
If you want to know, how to change OS in license... It depends on what how did you get a Directadmin. Did you buy a dedicated or VPS server with Directadmin? Or you have access in client area https://www.directadmin.com/clients/ ?
to update no worries, it is by cons about DirectAdmin, I have a dedicated server and I installed myself DirectAdmin. My license is purchased from my rental company server. I have a 5 digit number