Don't know your screen resolution? See below for how to find out.
Click the Apple icon in the top left along your task bar. Go to "System Preferences." Next, click "Displays." Find the list of available resolutions in the box to the left. Make sure this setting is set to the highest setting available.
Right-click the desktop, click "Screen Resolution." Drag the slider to the recommended location. Click "Apply" then click "OK."