How to delete UV mapping.

How to delete uv mapping or reset it.

In edit mode in 3dview, only select the faces you want to reset. Then press U and choose Reset.

Also, in the UV editor you can pin the vertices you wish to keep (select and press P). If you choose ‘Unwrap’ in the unwrap menu (U), the pinned vertices will keep it’s current UV position

You can also move the various face-shaped pieces of the map anywhere else you want them to be on the same map.

For simplicity, I usually use texture-painting to create a singe image that is used as a source-map for the entire object, and basically let the mapping be whatever is a convenient automagically-generated default. To build the map, I draw from other image sources that are appropriate for each surface of the object.