Follow the instructions in the below link for the OS X version you wish to reinstall. When the Utilities Menu appears select Disk Utility and click on the Continue button. Select the Recovery HD and click on the arrow button below the icon. Alternatively, restart the computer and after the chime press and hold down the OPTION key until the boot manager screen appears.
Restart the computer and after the chime press and hold down the COMMAND and R keys until the menu screen appears. The process you follow will require you boot from the Recovery HD: