The reason you cannot add spans or degree the way you expected is probably because you are using a version of alias below 2013, and therefore when you select the cube, you are actually selecting a group, of the 6 surfaces that make the cube because normal picking mode is OBJECT..UNGROUP the cube, an now you should have 6 ungrouped surfaces. While you do this, you can open your OBJECT LISTER and see what is going on.
If you pick select SURFACE you can select surfaces individually without ungrouping.
You can add spans to your surfaces in many ways....
Object INSERT, and you can insert rows of cv where you wish.
On the control panel on the right, you can quickly change degree and spans.
You can rebuild surfaces too, with surface edit REBUILD.
Hope that helped.
Good luck.
