Renewing Kyalamy

Hello everyone!
having time available I decided to spend it renewing a circuit I particularly like, Kyalamy.
what I would do besides changing the texture (I already knowhow to do it) is change the kerbs and the grass/gravel outside the track to make it more modern, but i need some help on how to do it, so if someone can explain me it would be very appreciate!

KERBS
i hate that really high kerbs in some turns, like this one on the picture

how can i lower that to a normal kerbs?

GRAVEL
how i change the outside of the track from gravel to tarmac?
and how i can apply a texture like the new first corner, to make this

look like this


Thanks to anyone who have some time to explain a noob of track editing