You need a separate condition for each key, if you want each key to do something unique. Note that you'll need to modify the frame number specified in _root.char.gotoAndStop(6) for each respective key press.
if (Key.isDown(Key.LEFT))
{
_x -= power;
_root.char.gotoAndStop(6);
} else if (Key.isDown(Key.DOWN))
{
_y += power;
_root.char.gotoAndStop(6);
} else if (Key.isDown(Key.RIGHT))
{
_x += power;
_root.char.gotoAndStop(6);
} else if (Key.isDown(Key.UP))
{
_y -= power;
_root.char.gotoAndStop(6);
}