Go here....
C:\Documents and Settings\All Users\Documents\Monolith Productions\FEAR
open up "settings.cfg" with Notepad
You should see these two lines somewhere
"ScreenWidth" "####"
"ScreenHeight" "####"
just put the resolution that you want within the quotes.
For 1920x1080 it would be this....
"ScreenWidth" "1920"
"ScreenHeight" "1080"
Just make sure you avoid going into the FEAR settings and changing the reoslution because since its technically not on the "supported resolutions" list, it will revert to the highest res supported....