shouldnt have to uninstall drivers since you didnt install any recently. to boot in safe mode hold down the F8 key when the computer is booting(its whats called the POST or power on self test)you should get a selection and choose "safe mode". it can easily be missed so just keep tapping F8 after the first inital screen, it should get you in there.
then just change the display properties from right clicking on the desktop and choosing properties but im guessing you know that already.
edit: it shouldnt apply in your case but if you had to uninstall the drivers its basically going into the "add/remove programs" menu in the control panel and uninstalling that particular driver from there. there are other ways but thats the easiest and best but again, just sounds to me that monitor/graphics card doesnt support that resolution and needs to be changed back.