upgrading 11.04 to 12.10

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http://askubuntu.com – I use 11.04 and want to upgrade to latest version 12.10. but cannot get either software centre manager or synaptic to open, I just get error messages. I have downloaded Iso of 11.10 for an incremental install, mounted it but it will not run. get an error message stating ' cannot find autorun file '. how to upgrade incremently? can I fix software centre? (HowTos)