The adress is: 8th district, 
"Corvin sétány 2B", the house itself is on a walkway (promenade), it's restricted for the traffic.

Either

You take the ASM (Airport Shutle Minibus) - there is a desk at the arrival, You can book Your departure transfer as well. (http://www.airportshuttle.hu/en/ )

Price: http://www.airportshuttle.hu/en/#prices (Appt. Is in the white zone – Return fare for two persons: 8790 HUF = cca. 30EUR)

Or

If You take a taxi, the price is about 22-25 EUR. (One way)

Tell the driver, he should drop You at „Futó utca 52”, at the Corvin Parking House. There is a gas-station as well.

The taxi will drive into the Futo street it will drop You out about 100 meters from the main entrance of the shoping mall „Corvin Plaza”

Walk to the main entrance of the mall and turn down to the Corvin walkway.

In the middle there is a ground-fountain (may be not working in winter).

You'll see two new blocks: "City Garden" on the right side and "Fontana" on the left. Walk to the middle (B) entrance of Fontana,

portal B, 8th floor, flat 4

pls. give me a call or sms , when You leave the airport!!!!