Unfortunately, if you have allowed them to take up residence in your home, either through a formal or informal agreement and they refuse to leave upon your request, you'll have to evict via the judicial system.
The first step is written notice of a violation of the lease with an opportunity to cure, or a notice to quit (stating that you do not intend to renew for the next rental term.) Choosing the correct notice is critical and is determined by the type tenancy and duration of the lease period. Evictions of this type are not simple and are very fact specific. You should consult with an avvo attorney regarding the specific facts of your case before getting started. This could save you from loosing in court based on a faulty notice.
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Mr. Eby is correct and I would suggest that you hire him. You are going to have to go through the eviction process of Serving them with a Notice to Vacate and then a Summons and Complaint in Unlawful Detainer.
The information provided in this answer does not create an attorney-client relationship and is not considered to be legal advice. Mr. Leroi answers questions on Avvo because he strongly believes in public service from his years as a judge, magistrate, and prosecutor. If you need to ask any follow up questions because my answer did not fully address your question, feel free to call Chris or post an additional question. Thank you.
The other commentators are correct. If they won't leave when you ask them to, then you'll need to go through the eviction process. You can find some forms and directions on the Colorado Judicial Branch website, but you'd be better served by talking to someone like Mr. Eby.