Carbuerettor cleaner will remove it after wiping the most off it first - available in aerosol form.
Or if you have slarried the whole engine in it - use gunk ( if they still make it ) brush on and blast off with power washer.
alternatively you can use the lazy method...which I often employ....just go for a drive...the heat will burn it off quickly. Don't worry though it won't catch fire, but it will smoke a little!
Whowhatwhy - Synthetic oil can catch fire with heat esp if it has been spilt on an ehaust manifold. You can still get Gunk so I would use this by applying it with an old brush on a warmish engine. I would just rinse it off carefully with water from a watering can as jet washer can get water where you dont want it.