Ubuntu – “The software on this computer is up to date” while upgrading 12.10 to 13.04

12.1013.04upgrade

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:

enter image description here

Question: how to fix this issue and upgrade 12.10 to 13.04?

Update

I tried @montazeri's command and cated release file. Here's the output:

enter image description here

Best Answer

Question here, have you tried looking at the System Settings > Software & Updates information? Specifically on the updates tab, look at the drop-down where it states:

Notify me of a new Ubuntu version:

If it does not say 'For any new version' but instead says anything else, then this would occur.

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