@AP.Newbie 

I dont check this section of the forums much, but did today and seen your question..  hopefully you got sorted ok

One thing to consider is that making the antenna bigger on the AP will improve signal slightly, however this isn't the magic fix, signal strength is not the end goal here.    WiFi communication is a 2 way street, namely traffic flows from the AP to the device, and vice versa.

Quite often people would put a massive db antenna on their AP and expect miracles, yes you will see a stronger signal from the AP.. however your ability to send back to the AP wont have changed.  

Its common to think putting a bigger antenna on will increase range also, yes you will be able to see the SSID from a lot farther away; but it wont be usable as you will be unable to send replies, unless you have the same antenna.