Once you pull the sleds out, the system will lose connection to the Drives. So backup your data to a different drive inside the system if upgrading, or simply pull it out and use a replacement from the store or Cold Storage.
Since SATA is the new Standard, use one of those since they're faster and more reliable than Molex Connection.
SATA, or for the Older Folk out there, Serial-ATA connectors, use a series of Pins made with, more likely, Copper (or less likely, Silver or Gold), and each pin is for different things such as Power and Data Lines.
To remove the HDD Sleds, there is a handle that pulls out by a Tensioned Switch, and once out you can Undo the Screws holding the Drive in place, and even replace it with an SSD (if you have a 2.5" Drive sled, that is) and get even more speed from the newly installed drive.
For the Internal HDD Sleds, you can simply pull out when the computer is inactive because the system is not intended to be ran when removing internal drives just like a regular desktop.
When removing the HDDs and replacing them, simply grab your Philips Driver and unfasten the screws retaining the HDD in place. This will allow you to properly replace your Server's HDD that's being replaced with a new, functional one, or an upgrade to the previous, functional one.
