Hi, log in to the server, open 'Services' and look the user configured in the column 'login as' (or something like that I don't remember how it shows in english).
You will need the password of this user to do the update, and if it's from an old version mabe you also need the postgre superuser password, this password was set on the initial installation of Qlik Sense.
Updating from a very old version can also give some issues with ecrtificates, in any case, be sure you have a backup of the server before you start so if anything fails at least you can recover the current state.
