Raising Rents on New 4 Plex in Colorado

Hello BP.

We close on a 4 Plex in Colorado Springs on Friday 28 JUN 13. The appraiser and agent both think we need to raise rents from $800.00 a month to 850 or 900 a month based on market rates.

Three tenants are on month to month leases. How much notice is required and how to the notices need to be delivered to comply with Colorado Law?

Any other advice from seasoned Colorado investors?

Thank you for your time.