The first model, the Hotswap HDD Sleds, simply opens with a latch at the top of the Front Panel. Once that is unlatched, pull it out and down and you have immediate access to the drives.

With the Internal HDD Sled Model, you can just disengage the latch for that panel and pull the side off of it. Make sure to pull forward on the side panel because going the wrong direction, you simply are unable to open it.