Grease on my disc break disc, help plz , will choose best anwser, asap?

i just took my bike in to get a tune up and install a couple new parts including new break pads. my back break is working awsome, but my front wasnt, when i realized there was grease on it, im thinking wiping it with a cloth with wd-40 on it cuz i know it kills grease, but its a lubricant so i thought i better ask first incase it will just make it worse.