Repair and change the colour of the leather of a Roche Bobois sofa

Hello,

We would like to renovate our leather sofa ROCHE BOIS. It is a monobloc sofa with 3 seats and pictures of it can be found.
The leather of the sofa is cracked, but above all it is worn and begins to lose its colour in places.
After browsing your forum and various information pages, we read that it was possible to change the color. As a result, my wife and I would like to take the opportunity to do the same.
Currently the base is chocolate and the cushions / armrests are cream, and we would like black for the base and dark grey for the rest of the elements.

Could you first give us a price estimate and the products required to do so.
On the other hand, is it difficult to do the work yourself? How long does it take?

Thank you in advance for your prompt response.