f you have no another administrator account in the system, you cannot sign in Windows to reset it. If your PC is on a domain, your system administrator must reset your password. If you're using a Microsoft account, you can reset your password online. For more info, go to the Reset your password o Windows 10 or Windows 7.
If you're using a local account, use your password hint as a reminder. If you've tried these suggestions and still can't sign in, you'll need to reinstall Windows.