You can use Mears Transportation, they have a shuttle that picks you up your resort and takes you to Universal. When you are about ready to leave you call and make arrangements to be picked up. You can call Mears and make the reservations. You can even do this with short notice, 24 or 48 hours this way if your plans change you can adjust accordingly.
I think that the cost is about $16 per person round trip.
You can also hire a town car service, the cost is about $80 round trip, or rent a car for the day.