Can't login after upgrade

Hello, I am new to Grav. I thought I will give it a try as I like the flat file idea. I used another one in the past and it was relatively easy to use. But Grav kind of surprise me! The terminologies used all sounds 'greek' to me. All I needed to do is to centre my image. But I found myself reading instructions and can't make head and tail what it is about. While on my site I decided to update my version. I went in the settings and clicked on some of the permission. Suddenly all the admin links on the left disappeared and I could no longer log in to my site. This is my last attempt. I am about to give up on Grav and go back to what I am used it. :(

How are you running it? Localhost or on some webhosting? It sounds like the permission issue is related to the ownership of files which, Grav being file-based, is very important. I suggest taking a look a the the docs that focus on this issue: https://learn.getgrav.org/troubleshooting/permissions