OS X Yosemite: Adjust your display’s resolution
Your display’s resolution determines the size of text and objects on your screen. By default, the resolution on your display is set to show the sharpest text and the most detailed images. While it’s best to use the default resolution, you can manually set the resolution to make text and objects appear larger on your screen, or adjust it to make text and objects appear smaller so you have more space on your screen.
Depending on how you adjust the resolution, some apps may not fit entirely on the screen. Using a scaled resolution may affect performance.
Set the resolution for your primary display
Choose Apple menu > System Preferences, click Displays, then click Display.
Select Scaled, then select one of the scaled resolution options.
Set the resolution for a connected display
If you have more than one display, additional resolution options are available.
After the display is connected, choose Apple menu > System Preferences, click Displays, then click Display.
Press the Option key while you click Scaled to see additional resolutions for the second display. Then select a scaled resolution option for the second display.