It’s not only a good idea, but an absolute must, to erase your personal data from your smartphone before selling or trading the device in for a new one. Here is how to completely wipe all of your personal data from your Android phone.
Samsung Phones: Start Settings > General Management > Reset
Other Android Phones: Settings App > System > Reset > Reset Phone > Confirm
If you cannot find the factory reset option on your Android some phones may require you to navigate to the Advanced section to get to the reset options.