In order to hard reset a Fly SX300, you should perform the following steps.
Remember! Hard reset will delete all the data on your device; pictures, contacts, messages, apps and more.
Fly SX300 device will be brought back to the default configuration of a brand new device.
1. Switch on the phone.
2. Tap in the code *#987*99#. Confirm by pressing Send.
3. Now wait for the phone to reset & restart.