could not upgrade vista home premium to ultimate

quy nguyen

Hi,
I bought new laptop that is windows vista home premium 64 bit. I try to
upgrade to vista ultimate 64 bit but it seems impossible. When i run DVD
vista ultimate the upgrade option is greyed out (disable) only option
install new one.
I believe that theoritically it is able to upgrade the windows vista home
premium to vistal ultimate. Why does it not allow me to do so?
I really want to get my laptop join to domain but I could not do it with
Vista home.
Thank you for any suggestion to help me out.