HTOTM: FUSION
Original Post
How To Make a Bumpmap Texture
Can Someone Show Me How To Turn A Normal Texture Into A Bumpmap Texture?
-[+]-. . : :-|K e n n y r a y|-: : . .-[+]-
Ok, to be honest the way you ask the question is a little ambiguous ;)

The short answer: there is no way to convert it, it requires a lot of redrawing.

Well I will go in to it for you anyway.
There are many times of textures:
- Diffuse maps, these are images like textures used on Uke and Tori
- Normal maps, these are images that specify the direction of the normal of a plane
- Displacement maps, these are images that specify the Z-offset relative to the normal of a plane.

There are also many other types of maps, eg specular, reflective, hardness (specularity width), sub-surface, alpha, etc. Toribash doesn't use them however, and actually the alpha map is baked in to the diffuse map.

Now here is where your question becomes a bit tricky, you say "normal texture" which is a term meaning a normal map. However I suspect you just mean the diffuse texture, and are saying it to mean "the texture that is usually used".

A diffuse map is made just by using a regular image. A normal map can be converted to a displacement map by using only the brightness or luminosity of the map. This is kind of inaccurate, but it works. As for converting the diffuse map in to a bump map, no such process exists. They are fundamentally different. If for example your diffuse map was a simple smiley face ":-)" then the eyes and mouth would be pushed in, but so would the nose! There is no correlation between the value of the diffuse and the bump map.

Eg here is one I found on the web; to the left is the diffuse, to the right is the normal map

There is no way to make that conversion automatically without the use of 3d models.

As such I suggest you either Google bump maps, or ask a professional texture artist.