There is a WMO plugin on MC-Net (although I'd suggest you to use actually repository WIP version, installation tutorial can be found here:
Use it to load WMO into Blender. Then create materials, apply textures as you'd normaly do and turn them to WMO materials. Then export it as a new WMO. Done. If you don't know how to apply textures and materials in Blender, Google Blender tutorials. If you don't know how to use WMO plugin functions, something is described in manual
here. The rest should be quite self-explanatory, but feel free to ask more questions.