1-Remove your Google Account.
If you can still access your device's Settings menu, you should manually remove your Google Account. Just open Settings, then tap Accounts & Backup. Tap Manage Accounts, then tap your Google Account. Tap Remove Account and confirm that you really want to remove it. Then follow the instructions on the screen to continue.
2-Remove your Samsung account.
Now tap on your Samsung account and then tap Remove account. Tap Remove Account again to confirm that you want to remove it. Tap Sign out and enter your password. Then tap Done.
3-Turn off your device.
When you have successfully removed both accounts, turn off your phone completely. Wait for the device to vibrate slightly to indicate that it is already turned off.
4-Connect a headset.
Connect a wired headset to your phone in case your device fails to start in recovery mode without this device.
5-Enter recovery mode.
Now press and hold the volume up button and the power button for 8 seconds. Once the Samsung logo appears, release both buttons and wait for your phone to go into recovery mode.
6-Perform the hard reset.
Use the Volume Down button to highlight Wipe Data / Factory Reset and press the Power button to select it.
7-Confirm the reset.
Highlight Factory Reset and press the Power button.
8-Reboot your phone.
After the reset, press the power button to restart the phone.