Somewhat belatedly here is some info on this topic.
On my model the speakers are removed by first removing the protective "screen". Removing this reveals the screws to remove the bezel - you will have to have a torx drive as I remember(http://en.wikipedia.org/wiki/Torx). After removing the bezel you will see the speaker attachment screws, also torx. Removing the speaker then only leaves disconnecting the Ford specific connector. I have attached photos of this process. I replaced both the door speakers and the rear speakers with the following from Crutchfield:
158GT1327A Sony XS-GT1327A 5-1/4" 2-way Speaker
113KFC1362 Kenwood KFC-1362 5-1/4" 3-Way Speaker
Crutchfield supplies the speaker connector adapter.
(as well I replaced the head unit with a MP3 capable model)