You could just stay in the hotel, but if you want to see Amsterdam you can either leave your bags at the hotel, or go check in early at the airport, then take the train into the center of town.

You could walk from the central station towards the old church (Oude Kerk) in the red light district - which is not the wall to wall debauchery the name might make it appear, but the oldest part of the town with the church, some interesting museums (including Our Lady in the Attic, a church (that seats 100 people easily) entirely hidden in the upper parts of an old building, from a time when Catholicism was suppressed and no public Catholic churches were allowed but a church whose door was unmarked was tolerated, souvenir shops, etc. You could leave the central station at 09:00, have a couple of hours walking around with a bit of lunch, and be back 2 hours before departure. If you've managed to check in, of course you need less time in the airport.