Megane CC TomTom Aerial

[cc3]

Hi Every one
Got myselfe a Megane CC 130 TCE Tom Tom.Car is absoloultly fine no Leaks (touch wood.No Battery drain,,
MPG could be a lot better,Hand book says it should improve after 2.0000 miles,Hmmmm,, Volvo said my desial would do 74 mpg what a laugh i got 45-50m.As the volvo forum testifies to this at least Renault tell the truth on MPG.
Anyway iwant to change that carbunkle of an aerial which is sat on the Boot.Question is how do i do this?? do i need a special aerial? With the car having built in TomTom.I have tried the forums but nothing anybody help please
Really appreciated
Cheers