Car rental from Disney resort to MIA

[MatthewsMommy]

Hi everyone! I need some help! We are going to Disney then driving to MIA for a cruise in Jan. Originally only going for 3 nights so had a car rented for those few days. We decided to extend our stay and we really don't need the car the whole week. I need to rent a car to drive to Miami first thing on a Sunday morning. What is the best way to do this? Thanks!