Digitally modify and improve artwork

I have book cover art that I paid for from an artist, but I am not happy with his work on the second cover. I would like to see if someone can digitally alter and improve it for a more realistic look, like the first cover. This is not to make large changes. Small tweaks, perhaps lighting changes, that sort of thing. (Reduced size copies attached. Book 1 is the good one. Book2 is the one that needs work.)