I upgraded from 15.10 to 16.04 through the distribution upgrade utility. At the end it said upgrade successful with some errors. I rebooted and I couldn't login at all. It was a login loop problem but I could solve it using this (https://askubuntu.com/a/761581/666490).
Now after I logged in, I was struck by the terrible resolution (1024x768). So I guessed maybe I need to install fglrx (I have AMD Radeon R5 not NVIDIA). That's when I knew it is not supported on 16.04 anymore. And the Radeon open-source driver is already pre-installed with 16.04 but it doesn't seem to be.
The resolution is terrible and I cannot increase it from System Settings.
What should I do?