How to reset Samsung L700 model mobile password?

If it is a GSM device (one that uses a SIM card) then you can do a master reset via code:

Samsung Master Reset:

CAUTION: A "master reset" changes the phone settings back to default. This process will erase all contacts, downloaded settings, and downloaded applications (ringtones, wallpapers, graphics, etc). This process cannot be undone.

Enter *2767*3855# from the standby screen. (You may need to remove the SIM before it will allow you to type the code in)