Most important part would be to make it grayscale first, then select all the "colored" clothes, like say a black jacket or whatever, then lighten or darken it so it is the same value as the skin. Statues are not painted, so everything on them is the same value. If you dont do this step then it will just look like a photo of a guy with a texture on top of him, instead of a statue.
After you do that you can simply overlay the texture on top. If the perspective is like a birds eye or worms eye view then make sure to adjust the perspective of the texture as well. To make him look giant you can implement some atmospheric perspective.