How to combine many faces into single face

I created a dice using a tutorial. When I export it I see that it has about 2500 faces. My problem is how to join all the faces of the dice, so it only has 6 faces in total, like a cube has. I want to add a function where the dice rolls and gives an outcome, so I am facing a problem to give numbers to the faces. Please suggest a way to combine the faces.
My dice link is http://www.sggame.bugs3.com/dice1.html

I can’t see the link, but I can assume some things:

  • the dice has some nice bevelling and the dots on the dice for the numbers are recessed into the face

So other than creating a new die from a cube and applying a texture with normal map on each face, you will not get it down to 6 faces.
The best option would be to

  • recreate the die from a simple cube
  • bevel or otherwise smooth the edges
  • give the die a base material
  • on each of the main faces apply a UV texture with the numbers on them, with normal mapping to make it look better by chiselling out the dots.

If that doesn’t help you, then you can merge vertices, collapse edges, or shrink wrap (retopologise) the die.

I see the animation. nice.

For realtime applications, it’s best to just make a lowpoly (I’d make it slightly more than 6 faces, but it’s up to you) and bake a normalmap. You can also bake a few other textures, like an Ambient Occlusion and Curvature (edge highlighting and cavity map combined) to aid in texturing it.
I personally use Xnormal for this, but you could use Blender itself.