From Heathrow Airport:

Travel on the Heathrow Express train service to Paddington mainline train station. Transfer to Paddington Underground Station and take the Bakerloo Line to Charing Cross mainline station. Travel on the Hastings line from Charing Cross. Book to St Leonards Warrior Square. There is a taxi service from St Leonards Warrior Square.

From Gatwick Airport:

Travel on the Hastings line from Gatwick airport mainline train station which can be located in the South Terminal. Book to St Leonards Warrior Square. There is a taxi service from St Leonards Warrior Square.