Heathrow Terminal 4 to National Express to Southhampton

I need help in getting from Heathrow to the National Express bus to Southhampton this coming summer. I will be arriving on Delta in Terminal 4. At least that is what the booking says right now. Can someone please tell me how to get from Terminal 4 to the National Express to Southhampton.

A couple of years ago we arrived at Terminal 3 and I remember it was a very, very long walk with luggage to the station to catch the National Express. I am hoping that it will be a shorter walk and easier from Terminal 4. Thank you for any help anyone can give me.

Magic...

http://www.nationalexpress.com/wherewego/airports/heathrow-airport.aspx