Administration - Installation - Core: Re: Upgrade ILIAs 5.2 manual install to ILIAS 5.4 Git install

First ensure that all your plugins are 5.4 supported. If not you will have to either find the newer version (likely on github.) or upgrade them yourself.

Are you using custom skins? If so ensure that those are updated to encompass new functionality in the system.

Pull down from Ilias Github, go to setup.php and upgrade your database (Depending on how many clients you have this could take a bit.)
login and refresh system languages you have installed and ensure that all your plugins were re-enabled. (Chances are if you're using a plugin that you had to upgrade you will have to upgrade its database as well.).

There are other things to consider as well, ilias 5.4 is compatible with PHP 7.0.x, 7.1.x, 7.2.x, 7.3.x, you will have to make sure that your PHP is at least at 7.0.

if anyone else has anything to add feel free!