Adjusting brightess on monitor

hi, i have a time monitor its about 4 year old, Im trying to adjust the brightness, its quite dark, i've tried the buttons on the monitor and its set at the highest setting, but its still very dark. i was just wondering if there was a setting in the control panel i could use, im sure i've done it before, i just cant remember where i did it!!! any help would be fab, many thanks bethanx