iFixit

Remove the antenna board near the front of the mini by pulling it straight up off the internal frame.

If necessary, remove the piece of tape securing the antenna leads to the internal frame.

Be sure to keep track of the springs under each of the three antenna boards.

Use the flat end of a spudger to pry the audio ribbon cable connector up off the audio board.

Remove the four Phillips screws securing the internal frame to the bottom housing.

The screw in the lower right corner of this image is recessed deep in the internal frame and longer than the other three screws. A flashlight and a thin screwdriver aid in removal.

Lift the internal frame off the bottom housing, starting at the rear edge, until you feel the concealed edge connector on the motherboard disconnect. Then lift straight off, minding the bluetooth and 802.11 antenna cables.

Simultaneously pull the tabs on each side of the RAM chip away from the center of the chip. These tabs lock the chip in place and releasing them will cause the chip to "pop" up.

Pull the RAM chip directly out from its connector.

If there are two RAM chips installed, repeat the above procedure for the second chip.