upgrade from 32 bit to 64 bit windows 2003

I am trying to upgrade windows 2003 32bit to 64bit and it seems like there is no upgrade option from the installation CD. Could someone help to understand better in this situation?

1) Could I do a repair in the 64 bit installation?
or
2) there is no way that I could upgrade from 32bit to 64 bit except by fresh installation ?