Update: I tried using the nodes. I couldnt call new texture either by clicking the open icon. That is to say when making a new texture image node and clicking on open then choosing the file cave3.jpg I was  still getting cave1.jpg on the node. Then I tried typing "3" in the texture name to replace and it worked. I managed to change my material to the new texture. cave3.jpg even showed up in the uv/image editor.... All was working fine! except...

When I importing to poser I was still getting the normal maps as diffuse map instead of cave3.jpg. I went and opened the mtl file and the material in it is still the normal texture. After deleting mtl several time I was still getting normal map for my materials in mtl file. The problem was coming from Blender. I shifted to blender internal render mode and cave3 and after a while I realized the texture in the texture modifier tab was set to be the normal map. under the image rollout menu in texture modifier tab, the image set as old cave.jpg and under the source: header it was set as the normal map.

So I guess I have figured  out now where was my problem was coming from. But to be honest I have no clue what's going in that programme. if the interface was less confusing I would get a clear picture of what I am doing.