If you are already logged into your account and you need to change a user's password, you can change password from command line.
- Open the command prompt
net user ACCOUNTNAME PASSWORDand hit ‘enter'
You'll need administrator privileges and run the command prompt as administrator.
To see a list of users, type
net user and hit ‘enter.'
You can leave the password prompt blank (just hit ‘enter') to essentially remove a password.
You'll get a confirmation when completed successfully – The command completed successfully.
If the account name has more than one word or is otherwise separated by white space, put the account name in quotes.
If you're having issues connecting to a network resource, login physically and type
net user username /ACTIVE and hit ‘enter.'
Securely Change Password From Command Line
If you've got someone over your shoulder, like the user you're assisting for example, you can prevent the new password from appearing in the command prompt for all to see.
net user ACCOUNTNAME * and hit ‘enter.' This will bring a prompt for you to enter the new password twice.
Since this is a command line option, you can also access the command line by rebooting into safe mode. The same thing applies to the Windows repair screen as well.
There are also plenty of tools if everyone is locked out. One of the more popular Windows password crackers based on rainbow tables is Ophcrack.