Importing FBX model with updated textures into unity creating duplicate textures when using “Extract Textures”

I am trying to figure out the best way to update models, textures and materials. I have a city model (city.fbx) that comes into unity with baked textures and materials from C4D. I bring it in to unity, extract the textures into a local folder called “Textures” and extract the materials into a local folder called “Materials”. Everything is remapped automatically by Unity. Let’s say I then update the model using a file syncing program which replaces city.fbx with the same model, but with updated textures. In this case, the textures have been updated to green, where as before they were blue textures. when I extract the textures into the local “Textures” folder, unity creates duplicate textures instead of replacing the old ones. So we now have buildingtexture (the old blue texture) & buildingtexture 1 (a new green texture) – what is the correct way to import the updated model so as to avoid this?