I want to seperate the cellar area of my house as another cell so I duplicated the house cell so I can edit out all the house area leaving just the cellar and then set up transitions from the cellar to the house. But how do I rename the duplicate cell, there's doesn't appear to be an option to do so.

The option should be under "Interior Data" (or something similar, not at my CK). I think it's about the third tab along.

If memory serves, in the Cell list, you can right-click, and select 'Edit' to bring up the Cell Data (Where you set things like the lighting); if that doesn't work, I think it's under world-->Cells for the same information.