For example, perform a full reset of the Samsung Galaxy J5
1) First you need to turn off the phone.
2) Press the volume addition key at the same time, home (oval below) and the power key, keep them all three before the Samsung logo appears, then release.
3) With the volume keys, select “wipe data / factory reset” in the list, and select the power key (possibly also with the Home key), in the next window select “ Yes ” in the same way. And lastly select “ reboot system now ”
Done, the phone will start with completely reset settings and remote user data, such as applications, contacts, etc.