Oh. My. God. You can't get any more useless than you already are.
From left to right: Antenna assembly with plug, rubber gasket, angled plastic piece to match angle of quarter panel, metal nut with half asses screw driver slots in it.
Close up of antenna assembly and round metal nut. The antenna assembly (the part that's in the trunk) has two (2) sets of threads on it. The smaller upper threads are for the antenna that you've apparently already managed to get off in a feat of amazing mechanical skill on your part, and larger threads below it that the round metal nut screws on to.
Remove this metal nut, and the plastic angled piece and rubber gasket will come off, and along with the nut removed from the trunk, the rest of the assembly will fall out. The trick is to unscrew the metal nut without spinning the angled plastic piece, as that will result in scrapped paint. I believe Mazda intented something like this:
to be used to remove the nut, however a pipe wrench will work fine, perhaps with a rag to protect the metal nut, if you ever intend on putting it back on.
Please print these pictures and instructions and hand them to your grandmother, as I'm sure even she is more mechanically inclined than you.