Ubuntu – Why I had redirected while downloading Ubuntu ISO

You can download the .torrent files for all versions from the alternative downloads page. Use any torrent client (including uTorrent) to then get the CD image (.iso) file with it.

Yes, just as upgrades from LTS to LTS are supported, upgrades from an intermediate release to the next LTS are supported.

Historically this is only supported by manually changing your apt sources, since update-manager / do-release-upgrade require you to go step by step.

But since 13.04 will go end of life before 12.10, we will need to skip over 13.04 in the upgrade path. This will be implemented on the server (and with an SRU of the update-manager package to 12.10) to show the direct upgrade as an available option.