13 pin towbar wiring for Alko ATC

My 59 plate Ford Mondeo estate has a single 7-pin towbar fitted.  We picked up our new van today, a Swift Challenger Sport 554, and it's got Alko advanced trailer control (ATC) fitted, for which we need 13 pins.  We fbought a 7 to 13 pin adaptor just to tow it home, but will want to change the towbar wiring over to 13 pins so we can make use of the ATC.  

What are our options?  Is it fairly straightforward?  Will it cost me an arm and a leg?

Thanks

Kev