aerial removal is usually a bit of both, inside and outside
lift the outer seal off - it should just clip in
inside the car, locate the aerial mountings and the earth strap and unbolt them, disconnect the cables (2 electrical and one for the aerial itself) then slide the aerial assembly out.
thats the inner seal, that will come off the car attached to the aerial - if you are planning on stripping the aerial down then you need to remove that nut but from what I remember you can still get the mast out and split the case of the unit without haveing to remove it.
Outside, remove the nut and rubber seal.
Inside boot, remove trim and disconnect everything you can see, I think there is just one screw or bolt to remove and the unit is then freed from positioning slots, tilted to the side and removed, Very easy and obvious how it comes out.
There is a chance your alarm will go off when you disconnect the electric’s, that is what mine dose.