You can reach Forum Istanbul Shopping Mall directly by the subway that runs on "Atatürk Airport - Yenikapi" line and get off at the "Kocatepe" stop.
There is a bus stop right outside Barton Square which you can walk easily to the Centre.
From the Anatolian side; first take Marmaray (tube) and get off at "Yenikapı" stop and transfer to the subway that runs on "Yenikapi - Atatürk Airport" line and get off at the ""Kocatepe" stop.
From the TEM highway, make a turn at "Hal - Otogar" exit and follow the "Kuru Gıda Hali - Otogar" route. Or, from the E5 highway, make a turn at "Otogar" and follow the "Kartaltepe -Yıldırım - Kocatepe" route. There are 5000 free parking spaces at Forum Istanbul Mall.
Take the 32 (Cevatpaşa - Eminönü), 32 A(Cevatpaşa - Beyazıt), 32 M (Mecidiyeköy - Cevatpaşa or 32 T (Cevatpaşa -Taksim) IETT bus.
Take the metrobus and get off at the "Merter"" junction" stop and transfer to the subway station. Take the "Atatürk Airport - Yenikapi" subway and get off at the "Kocatepe" stop.