Open the Case Shut down your Mac Pro, give it a few minutes to cool off, and unplug all the wires and cables. Locate the latch on the back of the case and pull it out. The latch lifts out very easily and stops after an inch or two — do not try to force it any farther.
Opening this latch releases the side panel of your Mac Pro, which you should now be able to easily lift away from the case. Take it off and put it in a safe place
With the Mac Pro’s case now open, locate the four hard drive bays in the top half of the case.
Each bay has a number stamped on it, and they go in order from left to right. Bay #1 should contain the stock hard drive that was installed by Apple. Gently remove the bracket from the next empty hard drive bay — if you only purchased one hard drive with your computer, this should be bay it should easily slide out.
Remove your new hard drive from its packaging and use a phillips head screw drive to attach it to the bracket. Use the screws that are already included on the bracket.