OKW is correct. To clarify though, you need to take the airport's SOUTH exit to get to TOLL 417/Central Florida Greeneway aka "The Greeneway". There will be two toll plazas with $1.00 tolls each. Use exit #6 which gets you off onto SR536 which will take you to the Vistana on SR535.
If you take the airport's NORTH exit, you would head west on TOLL 528/Beachline Expressway aka "The Beachline" and there would be two toll plazas priced at $ .75 each. You'd merge onto westbound I-4 and the very next exit would be SR535 (Lake Buena Vista/Kissimmee) where you'd turn left onto 535 and the Sheraton Vistana would be ahead on your right.
BobK/Orlando