UPDATE a value field for area of the geom and convert sq m to acres using cartodb

I’m trying to use the SQL commands in CartoDB to UPDATE a value field that shows total acres of the area of the_geom. My SQL is pretty poor/entry level and has some issues:

UPDATE table_name SET shape_area=(SELECT ST_Area(the_geom::geography) area_sqm 
FROM table_name)

I’m missing something… any help?