You can file for a modification of the visitation to supervised visitation only. However, at 6 and 8, I think the boys are old enough to tell you of any problems. Unless you see any actual endangerment of the children, I would leave as is. It is only one day a week and no overnights so it is already very restrictive. Without showing some actual abuse or drug problems, the court may not change and you will have wasted a lot of time and effort. Wait until you have more.
Here are the forms
http://www.courts.state.co.us/Forms/SubCategory.cfm/Category/Domestic
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