NOTE: You may have to wait 30 seconds-1 minute when performing each step.
If you don't want to lose DATA there may be a "Forgot password?" option in which case google will reset the password via your email. If this option is not there then follow these steps.
To perform factory/hard reset please follow those steps (you will lose everything):
1. Turn the power off.
2. Press and Hold the Volume Up and Power button at the same time.
3. When the start up screen show (Samsung logo displays on the screen), release all the buttons.
4. Use the Volume Up/Down button to navigate to "wipe data/factory reset", select with Power button
5. Select "wipe data/factory reset"
6. Select "Yes -- delete all user data"
Allow several minutes for the factory data reset process to complete.
7. Select "reboot system now"
Allow several minutes for the reboot process to complete.