Make sure the system is turned off and unplugged from the mains before removing the case, and your hands are grounded before touching anything.

Then just insert the disk into the slot, (you may need slot sliders on the new drive but you will be able to see what the other disks are using), connect the power lead and data lead, and start up. The BIOS should recognise the new hard disk immediately.

Is there any reason you mention RAID?

Mark