screen resolution: is it safe to change?

[Oathkeeper29]

there's this monitor I have that is 17 in, so I thought it was set in 1024x768 in default... turns out, its in 800x600... I want to change it to 1024x768 but is is safe? I have an older monitor that has color distortion and lagging graphics and it might have been because of setting it from 800x600 to 1024x768
please help me!!!