Requirements:
1. Custom recovery with embedded file manager like TWRP. For other recovery, you can install AROMA file manager. Google how to install it.
Instructions:
1. Go to mount option then mount /system.
2. After that, open file manager, locate data/system/gesture.key if you use gesture, or password.key if you use password or pincode. Delete password.key or gesture.key.
3.Reboot.
Thats all!
Your pass or pin sure is already deleted.