How much can I legally raise the rent for my Boulder County Colo. house? Lease was up last June; now mo.-mo.?

When you raise the rent in Boulder County Colorado, do you have to legally use a certain percentage of the original rent? Is it based on the number of months having rented it? The lease was Dec 2006- June 2007 and has since reverted to month-month. I am an individual renting out my house while out of state. Thank you.