Same model, multiple resolution textures

For a mobile game I am working on.
I have a model from our 3D artist, which contains 256/512/1024 versions of a the same texture.

How can I tell unity which texture to use? Do I have to do it manually, or is there some magic naming convention that will cause it to use the correct texture?

Unity seems to be doing the right thing automatically, but not it’s a bit of a blackbox so I’m wondering if anyone can shed some light on it

I didn’t get what is your intention. In general case yes, you need to change manually each texture (because only you know when you want to use each).

But if you intention to use different texture depending of distance, you can search for mipmaps. There is some optionzations and unity3d and opengl.

As always is better to profile before do changes.