First, check your monitor's manual to find the desired resolution / refresh rate combination. Using unsupported settings can damage your computer.
Right-click on any empty area on your desktop. Select "Properties". Select the "Settings" tab. In the lower left-hand corner you will see an area labeled "Screen resolution" - drag the slider across until you reach your desired resolution.
Follow the above steps until you get to the "Settings" tab. Select the "Advanced" button in the lower right-hand corner. Select the "Monitor" tab. Select your desired refresh rate in the drop-down box.