Adjusting Your Screen Size in Mac OS X
TO ADJUST YOUR SCREEN SIZE IN MAC OS X, click on the System Preferences icon in your dock. From there, open the Displays item (under Hardware) and select one of the available resolutions.
Step 1: Call Up the System Preferences
Click on the System Preferences icon on your OS X dock: it's the icon with an Apple logo and a light switch.
Step 2: Select Displays
Step 3: Select a new Resolution