Go to Settings -> Privacy -> Location Services -> Move the slider to the right to disable the GPS, or to the left, to enable it.
Also, you can enable or disable the GPS to individual applications using each application's individual ON/OFF slider.
Note: Most mobile devices require the GPS feature to be enabled, as part of the anti-theft option, which allows you to locate your device if it's been lost in stolen. Bear this in mind before you decide to disable the location service.
If you don’t receive the email in the next 2 minutes please check your junk folder, and add [email protected] to your safe sender list.