The international airport of Sao Paulo is Gurarulhos which is 25 km north-east of the downtown. The easiest way to get to downtown is by hire car or taxi. Please also note that driving in the city can become difficult, to say the least, as the traffic is often heavy and driving standards are erratic.
In additon an airport bus runs every 30 minutes, though travel can be quite uncomfortable when buses are crowded.
The easiest way to get to the circuit is by taxi or by hire car (with the reservations above).