What's the fastest way to change textures for 100 objects? I had to convert all my PNGs to JPGs, reason why now I need to switch to those new texture files. 
Batch converting the image files was easy and fast. But how to do the next step in Blender now?

Thanks in advance guys 

DPC
You can replace the filepaths using python and then reloading the images:

import bpy
for img in bpy.data.images:
    img.filepath = img.filepath.replace('.jpg', '.png')
    img.reload()