In order to hard reset a Ericsson GF 788e, you should perform the following steps.
Remember! Hard reset will delete all the data on your device; pictures, contacts, messages, apps and more.
Ericsson GF 788e device will be brought back to the default configuration of a brand new device.
1. Turn the phone on.
2. Select Settings and Master Reset (press Yes to select/confirm).
3. Now enter the phone's lock code (0000 by default).
4. Confirm the operation. Done.