tried gimp within the first hour, the exe they had me download wouldn't open.

Alright I've been at this for hours, I've got a migraine, and I'm very much out of patience, so I'll try to say this as politely as I can.
I'm working on a Rindo Avatar for someone and they want the texture to be NSFW but everywhere i look no one has it, all people do is tell me to "edit the psd in photoshop" whatever that means. One: I can't afford photoshop, two: even if i could none of that makes sense to me, so if there's someone out there who can actually friggin help me with this, I'd appreciate it