If you’re using Windows XP/vista/7, and in some case you want to change your Administrator’s account password, you’ll need to know the current password before you can change it,showing as below.
If you go to Computer Management from Control Panel -> Administrative Tools, you’re able to RESET the password without knowing the current password! However, this way of resetting your password might cause an irreversible loss of information. For security
reasons, Windows protects certain information by making it impossible to access if the password is reset. So it’s a risk doing that.
There is another way to Reset your Windows xp/vista/7 administrator password Without knowing it,and very simply,requires only a simple command.
Just open cmd>type>cmd and type: net user *yourusername* *newpassword you want to set*
Enter,and it ok now.
Note:Reset Windows vista/Windows 7 password may need admin rights.just run the cmd as administrator