On the login page, select the link typically labeled Forgot Password or "Reset Password".
If you created a reset disk previously, insert the USB, click Reset password on the login screen, and follow the wizard. Reset password
At the sign-in screen, select I forgot my password and follow the prompts to verify your identity online. On the login page, select the link typically
If locked out and without a disk, you can sometimes use the command net user [username] [newpassword] via the Advanced Boot Options (Safe Mode with Command Prompt). On the login page
For a visual walkthrough on resetting a forgotten Windows password using the command prompt:
Click the link in the email, enter your new password, and confirm it. Windows PC Passwords