HF upgrade from v6.6 to v 7.3.3

Hi All, I am planning to upgrade a heavy forwarder from v6.6.6 to v 7.3.3 What should be my approach to upgrade? Can i directly upgrade the HF to v 7.3.3 or, I have to upgrade it to v7.0 and then to v7.3.3 Please help. Thanks. Regards, Abhi