In order to hard reset a BlackBerry 6720, you should perform the following steps.
Remember! Hard reset will delete all the data on your device; pictures, contacts, messages, apps and more.
BlackBerry 6720 device will be brought back to the default configuration of a brand new device.
1. Switch on the phone.
2. Go to Options and then to Security.
3. When there, press Enter.
4. Select Wipe Handheld, followed by Continue and Enter BlackBerry.
5. Your phone will reset, all of its content erased. Congrats, the hard reset process is complete.