The phone you currently posses is running on Android and this operating system provides simple ways to restore the device to the factory default state. One is by going into the system’s settings and use a built-in function and the other one is related to the Recovery menu which is accessible by pressing a combination of buttons (Volume Down + Menu Button + Power button). In graphic mode, locate settings on your main menu and go to Privacy and click on Factory Data Reset. It will erase all data on phone including applications, settings, etc. In recovery menu use the buttons to navigate and select Wipe Data/ Factory Reset and restart your phone.