upgradtion of versions of Fedora

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http://www.unix.com – I am using Fedora 15 Lovelock. Along with I have windows 7 as another os using dual booting. I want to upgrade fedora from 15 to higher version. If I do it using the cd of fedora there is a chance that 7 will be omitted. I want to keep both. So what can be done? (HowTos)