This is step to upgrade ubuntu offline via ISO than you can do with any version of ubuntu.
1. First you must have an alternate ISO file of ubuntu any version. Alternate Iso is different with Desktop ISO. I want to upgrade to ubuntu 9.04, so i must have Ubuntu Alternate 9.04 IDO file. You can dowload it here.
2. Then you must mount it in cdrom with this command :
sudo mount -o loop ~/Desktop/ubuntu-9.04-alternate-i386.iso /media/cdrom0
3. After that you run this command as root
gksu “sh /cdrom/cdromupgrade”
4. Then it will show upgrade window and you can go configure it easily.