The exact directions from Denver via google maps are here, but the general directions are to take I-70 West for just under 90 miles. Then take exit 195 to merge onto CO-91 S toward Copper Mountain/
For a (slightly longer) alternative, especially if you prefer to avoid the tallest mountain passes, you can also take I-70 West from Denver all the way to Glenwood Springs (about 170 miles). Then follow signs to Aspen on CO-82 East for about 40 miles.
Cell service on the road can be spotty in places, so we recommend that you print out some directions (or load them on your phone) when you have service.