Factory reset your Android phone from the Settings menu

N.B: Be sure to back up your entire phone's data beforehand. Embarking on this process      means erasing all saved data on your android phone.

1. In the Settings menu, find Backup & reset, then tap Factory data reset and Reset phone.
2. You'll be prompted to enter your pass code and then to Erase everything.
3. Once that is done, select the option to reboot your phone.
4. Then, you can restore your phone's data.

Factory reset Android in Recovery Mode

If your phone is so messed up that you can't access your Settings menu, there's still hope. You can reset in Recovery mode, using just the buttons of your phone.

1. Turn your phone off.
2. Hold the Lower volume button, and while doing so, also hold the Power button until the phone turns on.
3. You'll see the word Start, and then you should press Lower volume button until Recovery mode is highlighted.
4. Now press the Power button to start recovery mode. You should see an Android robot now.
5. Once you're in Recovery mode, press and hold the Power button, and while doing so, press the Upper volume button once, then let go of the Power button.
6. Press Lower volumes until Wipe data/factory reset is highlighted, and then press the Power button to select it. 
7. Once that's done, press the Power button to select Reboot system now.
8. Then, you can restore your phone's data.