In order to hard reset a Ericsson GS 337, you should perform the following steps.
Remember! Hard reset will delete all the data on your device; pictures, contacts, messages, apps and more.
Ericsson GS 337 device will be brought back to the default configuration of a brand new device.
1. Turn on the phone.
2. Open Settings and Master Reset.
3. Type in the phone's lock code (0000 by default).
4. Confirm. Done, the hard reset is complete.