Change Motorhome listing from Classified to Auction

Hi, does anyone know how to change a Motorhome listing from a Classified type to an Auction?

There doesn't seem an option to do this when editing the classified, although it is still running so I will wait until it expires and then see if I can change it at the time of relisting.

I want to be able to keep all of the followers on it that I currently have - hence not wanting to do a completely new listing.

Cheers.