This seems like a very straight forward item but a lot of people get confused with how to activate ConfigMgr after installation and the 180 trial starts to run low. Luckily this is a rather easy process and simply requires you to launch the “Configuration Manager Setup” from the start menu or start screen on your server and follow the below screenshots.
1) Launch Setup from the start menu or start screen.
2) Select next in the setup wizard screen.
3) Select “Perform site maintenance or reset this site” and click next.
4) Enter your license key and select next. If the option to upgrade to a licensed version is not present than you have already completed this step.
Please be aware that should you let the evaluation period slide that the only option is Recover a site, and it will go through a different process but eventually get around to asking for the key.
And in post recovery be sure to have any and all CUs available as it will let you know that you will need to re-install them.