How to unlock screen If you forgot password on Windows Phone 8
You have to reset your phone to factory settings to unlock screen. There is no other way to reset lock screen password. If you reset your phone, You will lose all the data like photos, videos, contacts, sms etc. If you have cloud backup enabled, you can restore data from backup after resetting Windows Phone.
You can't use soft reset as you can't get past the lock screen. You need to hard reset phone using hardware keys like Volume, Power buttons. It is very easy to hard reset Windows Phone. It does not take long to reset phone. You can read instructions for hard resetting Windows Phone 8 here
One of the features of Find My Phone on Windows Phone site is Erase. You can erase or reset your phone remotely by logging into Windows Phone account. on the Microsoft Windows Phone website.
Go to Windows Phone - Find My Phone
page and login with your Microsoft or Hotmail or Xbox or Outlook account you used on your Windows Phone. You can do this on your computer. You will see the option to Erase
your phone. Microsoft sends a sms message to your phone to erase your phone.
If you have push notifications turned on under "Settings > Find My Phone > Send apps to my phone using push notifications (not SMS), You can erase phone If you just have WiFi on your phone and don't need to have cellular signal.
Your will be returned to factory settings. You will need to setup your phone again.
These methods should work on any Windows Phone 8 including Lumia 920, Lumia 820, Lumia 810, HTC 8x, Samsung Ativ etc