Finding Texture In A 'Manystack'

I can not figure out the code for this to save my life…

I have a model with multiple textures and multiple materials.

I want to find one specific texture on the model and load another texture in its place, without changing anything else.

Can someone show me some simple code for doing that? As a python user.

PS. If there’s a way to locate a specific material and do the same thing…please share the wealth. That’s something else I might want to do in the future.