1. Login to guest or any other account where you have access
2. Open command prompt and then type: net user (or) net users
3. It will the show list of users
4. From the list of users, you can pick up one.
5. And then type: net sam * (assuming sam as username, replace sam by the username you get from the list)
6. After the execution of the command, it will prompt you to type the password. when you type password, the password you’re typing is not shown. So type the password carefully.
7. After typed, it will prompt you again to confirm the password.
8. Then press enter key, now the password of that particular user will be changed.