There are 2 malls basically attached to the hotel with a huge variety of ATMs, banks and money exchangers.
Walking outside, via the rear doors, turn lest and go into Centennial Mall and there is a small lobby with 3 or 4 ATMs just tot the right of the main entrance, in the middle of the mall on the ground level.

nearest money changer- exit the hotel from the rear doors (rather than the main entrance with valet, driveway etc) and cross the road. Take the escalator or lift up, and walk out as Ross the path to glass double doors which are the entrance to marina square mall.
the money change (fountain money changer) is basically right in the doorway on your left.