[ubuntu-in] Upgrading to Ubuntu-9.04 - using iso image

[consoleart]

Hi All,

I have downloaded ubuntu 9.04 iso image, i already have 8.10 and want to 
upgrade, i cannot use a network upgrade due to internet restrictions at 
my work place.

Please guide me how to upgrade to 9.10 using the iso image that i have 
downloaded.

I have written the same on CD and when i inser the CD it does not ask 
for any upgrade.

Regards
Jag