According to Einstein theory, approaching the speed of light the time is flowing slower due to Lorenz dilation (see twin paradox). Furthermore going faster than light (that is not possible) the time should starts flowing backward. Unfortunately to accelerate a body to the speed of the light you need infinite energy, unless the mass of the body is zero (like photons). Other way to travel along the time is to take advantage of strong space-time curvature (black holes). Of course this is only a theory. You can have a look at the Gödel, Tipler or Gott time machines.