Upgrade Ubuntu option not availiable when installing from USB stick!

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http://www.linuxquestions.org – I want to upgrade my current O.S. Ubuntu 13.04 to Ubuntu 13.10. For that purpose I created bootable usb stick using unetbootin. When the laptop boots, it boots from the usb. Now after a few steps there comes options as how to install. Here there isn't the option for upgrading ubuntu which is supposed to be there as clear from this installation manual of Ubuntu. For your ease I'm showing the options as mentioned in the manual below. Attachment 14368 Please see the image below that shows what I get when my usb stick boots. It's not having the option for upgrading. (Why that option isn't appearin (HowTos)