Hye you will have to follow these steps:
Click Restart at the login window
While the computer is restarting, hold down "Command-S" until you see text scrolling through the window.
This boots the computer into single user mode.
At the Localhost% prompt type:
/sbin/mount -uw //sbin/SystemStarter
You will then see various services starting up.
When the Localhost% prompt reappears, type:
passwd root
It will then ask you to type the new root password twice, so do so.
After entering the new password, type:
reboot
At the login window, enter username root wih the new password.
Once you are connected, you can use the Multiple Users application (/Applications/Utilities) to change your normal user's password, or create a new user account.