HaloMods "Classic" Read-only Archive

alright i dont know if you can do this but what do i need to change the _bump of the skin
ex. coag_cliffs_bump

do i need a plugin for photoshop? do i use paint pro x?
any help is appreciated

i think it's done with alpha channels, in photoshop.

i'd go for photoshop, most tutorials i have seen are for photoshop