3 methods ....
Using Moodle Admin interface - which does require your moodle to share info with Moodle.org's plugins server.
Manual - server admin finds the compatible .zip file, downloads, then manually places zip in proper directory and unzips. Checks ownerships/permissions on extracted plugin. Can then use either web based install (which updates DB tables) or the cli script in code/admin/cli/ to install (upgrade.php)
Git - must use git to acquire the code and git to update code. CLI only to acquire ... can use CLI or GUI to install (update DB).
Which is better .... depends upon admin perferences and comfort level ... + access level to server and if admin suffers from 'clas' .. ' command line avoidance syndrome' or not.
All the above dependent upon hosting and level of access to server.
So .... ?????
'SoS', Ken