The Airport Express shuttle is free from HK station, with the train ticket from HKG to HK station, but drops you off between the Ren and GH, actually at the entrance to the convention center. There are a few stairs to take, going the most direct route, not bad as long as you're traveling light. Otherwise, a taxi was about HK$30 from HK station to the GH. You'll have more help than you may need that way, as you will be at the GH front entrance.