You will need a putty knife or small paint scraper to remove the Mac Mini's casing, a small Phillips head #2 screwdriver, a pair of tweezers, and either a replacement 2.5-inch solid-state drive or a hard drive. It also doesn't hurt to pick up a can of compressed air to clean away the dust.
There are three orange antennas that must be removed before moving forward. The two on the left simply lift out, while the larger one is held in place with a clip that must be squeezed from the bottom.
Secure the hard drive in place, reattach the temperature sensors, and place the CD drive back into the case. Use the four screws to secure the CD drive, and reattach the ribbon cable. Then, take the three springs you removed earlier and place them back on their corresponding antenna posts, followed by the antennas themselves. Place the case back on the Mac Mini and push down evenly along the edges to lock it in.