It will take about 5min walking.

Leave the Sheraton to the bridge connecting to long distance train station.
Donīt turn right to station but go straight and make your way down to street level. Now just follow the T1 building passing buy Taxis and Hotel Shuttles and FCT is on your left. Ring downstairs and somebody will open or take spiral staircase outside the building if you have no luggage to main entrance.

Unless it is heavily raining in my eyes absolutely worth the walk as you will saye time on security and transfer to plane.