If the solution is posted here already - sorry, couldn't find it.
I spend whole hour to find it so... why not post here.
I was seriously furious because no matter what the game didn't respond to changes in GameUserSettings.ini .
I've changed FullscreenMode=1 to FullscreenMode=0 and... game is running in 1920x1080 as I wanted!
Just a reminder - set file as "Read-only".
Anyone now how to tweak GameUserSettings.ini further to achive better graphics?