Gently bend the Jimmy outwards to pry the crack open a little larger and lift the lower housing up a small amount.
There are several plastic clips on the lower housing that fit into a channel in the aluminum top housing. Your goal is to use the Jimmy to push these clips inward enough to free them from the channel, while gently pulling up on the lower housing.
In the next few steps you will be removing the AirPort and Bluetooth antennas (shown in red) from the internal frame. Be very careful, as breaking the brackets will require replacing the internal frame.
We will first remove the AirPort antenna, located in the lower left corner of this picture.
Remove the following four screws securing the internal frame to the bottom housing:
Three 6.7 mm Phillips #00 screws
One 9.5 mm Phillips #00 screw
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.
When reassembling, the wifi antenna wire routes to the inside of the vent and then over the top of the vent.
Use the flat end of a spudger to pry the three antenna connectors off the AirPort/Bluetooth combo card.
The black/blue antenna cable attaches to the AirPort card near the corner of the mini, and the white antenna cable attaches nearest the center of the mini.
This card is unsupported in macOS Sierra, so this device is outdated by Apple, however folks have been able to replace the card by a "compatible card" and patch the macOS Sierra install app, to actually install sierra on this version of the Mac.
I would appreciate if iFixit could provide a guide as to which cards could work, especially in terms of the size/dimensions, in this unit.
I just successfully upgraded my Mac Mini 3,1 (Early 2009) to the BCM943224PCIEBT from a Unibody MacBook A1278 and everything works swimmingly on macOS Sierra 10.12.
As an Apple Certified Mac Technician, I can tell you that this has by far been the most challenging replacement I have ever done.
There are two hurdles to overcome. First is that the MacBook card is shorter, second is that the uFL connector from the antennas are slightly shorter than the connection on the new board, so I had to really jerry-rig it in there with a bunch of electrical tape.
I will be posting a write up sometime soon, and will update you when its done. In the meantime, go buy the card from eBay for $5 https://is.gd/PxYlLt