Step 1: Launch Command Prompt: Start -> In search box, type in: cmd.exe -> Right click cmd.exe on search result -> Run as administrator. If you are login windows with administrator user, you can run cmd.exe directly without "Run as administrator".
Step 2: On Command Prompt, type in: Net user <user name> <new password>. Tips: Replace <user name> with user name, and replace <new password> with password. When get message "Command completed successfully", it means the password has been reset successfully.