Is there a forgot password option on the lock screen? Sometimes you can use your Google account to reset the password.
If not, you can factory reset your device using the following steps:
# Power off your device, and hold the volume down key and the power/lock key simultaneously for a few seconds.
# In recovery, there will be a “wipe data/factory reset” option you can select. Use the volume keys to navigate and the power button to select a menu option. '''This will wipe all data on the device!'''
Hope it helps!