|Easy and best may be different.|
Easy may be to delete the account with some live cd. See petri site for some ways that are still valid. search petri change password.
Best is to know how to recover the system back to OEM state. Owners manual should provide options. I never back down from a complete reload. At some point you may need to know how and might as well be today. Your personal data may be lost along with programs so you really need to know what you are doing before you start that.
"The era of big government is over," said Clinton 1996