Not too hard to do, although a little more complicated than it should be.

1. Select the object -- make sure you are in object mode.
2. Select the UV set you want to copy. Right-click model, UV Sets, select the one you want to copy.
3. Go to Edit Polygons | Texture | Copy Current UV Set Options Box.
4. Type in the name of the target UV set you want to copy to.
5. Re-select the previous UV set.
6. Delete that UV set with Edit Polygons | Texture | Delete Current UV Set.

Voila! One UV set.