Rotors can always be cleaned; sometimes you have to use scotch brite or sandpaper, but usually brake cleaner alone will clean them fine. Make sure you clean the areas around the rotor, especially the hub, to make sure the contamination doesn't drip, "sling" or migrate back onto the rotor. The best brake cleaner is perchloroethylene (original red-can Brakleen) because it is non-flammable and relatively gentle on rubber, paint, aluminum etc.; however all commercial brake cleaners clean the brake rotors themselves just as well. If you don't have brake cleaner you can try alcohol or degreasers.
The brake pads may be ruined. You can try drenching them in solvent or sanding them down slightly, but it might be better to just get new ones. If you use contaminated pads, you will have to repeat cleaning the rotor, so trying to rehabilitate brake pads is often not worth it.