If you have forgotten the security code, then there is no other option than formatting the phone completely to its factory settings. For this, follow these steps.
1) Switch off your phone and remove the SIM card as well as micro SD card (if any).
2) Now, at a time, hold down these keys: *, 3, green (call) button.
3) Keeping these buttons pressed, switch on your mobile.
Note: Do not leave any of the three holded keys till the phone starts resetting.
Your phone will now be reset to the original factory settings. Enjoy!
"For quitters never win, for winners never quit"
Syed Musaddiq Andrabi