Before you guys close this question as duplicate, I did go through How do I upgrade from 12.10 to 13.04? and nothing solves my problem there.
When I try to upgrade my ubuntu 12.10 installation it says
The software on this computer is up to date.
There are no upgrades available for your system. The upgrade will now be canceled.
Here's a snapshot:
Question: how to fix this issue and upgrade 12.10 to 13.04?
I tried @montazeri's command and cated release file. Here's the output: