There are escalators and travelators at Schiphol. At Amsterdam C, there are escalators and lifts, but you may need to walk along the platform to get to them. Best way is to head forward (in direction of travel) and find the lifts there - they may be past the front of the train. This will tags you to the east tunnel, which is the closest to the Doubletree anyway.

Dead easy - I'd always opt for the train, personally.