its quite simple to remove the aerial mast,
undo the nut ontop of the aerial, , turn the radio on and at the same time hold down FM button, this will show (or should) display antenna on the display, the aerial , will go all the way up, feed the antenna out , stick new aerial in , i think teeth facing front , get some one to turn off the ignition, aerial should retract, stick nut back on , and test. that should work :)
took me minutes to do mine ,