UPDATE public.mytable SET
jsonfieldname = jsonb_set( jsonfieldname, '{json_obj_key}', array_to_json(
	array_remove( ARRAY(
		SELECT json_array_elements_text( COALESCE( jsonfieldname::json->'json_obj_key', '[]' ) )
	), 'Element to remove' )
)::jsonb )
WHERE id = 23
RETURNING *;