How do you add the dirt texture to a track

[Bigfoot 57]

I have downloaded the Fontney track along with the Dirty old town skin which seems to contain nothing but dds files inside about 6 sub directories why so many
Anyway all I want to do is map the original tarmac surface into the dirt skin to make it look more authentic with the cars I’m using
I’m perfectly ok with editing any ini files that might need tweaking I just need somebody to explain how you get a new surface mapped onto the old one maybe a dum question but I’m new to this having joined your forum on the 3rd April

Regards

Colin