If you are a Fedora using running Fedora 15 or even Fedora 14 and want to upgrade to the latest, and the greatest, version of Fedora, you can easily do that using PreUpgrade. The goal of PreUpgrade is to provide a way for Fedora users who wish to upgrade from one release to a newer version of Fedora by easily pre-resolving and downloading all the necessary packages before rebooting the system into the Fedora installer to complete the update.

Hop on Hop Off
If you are using Ubuntu you can only upgrade to the next version. For example, to upgrade from Ubuntu 8.10 to Ubuntu 9.10, first upgrade to 9.04, then upgrade 9.04 to 9.10 you can't skip the version. This is not the case with Fedora -- thanks to PreUpgrade.

Preupgrade provides an upgrade directly to the latest version of Fedora. It is not necessary to upgrade to intermediate versions. For example, it is possible to go from Fedora 11 to Fedora 13 directly. PreUpgrade is stable and is available in all current Fedora releases. While PreUpgrade downloads the necessary packages, users are free to continue using their systems. This gives an experience similar to a live upgrade.

Fedora team has published a detailed guide about using PreUpgrade to upgrade your system. Read the guide here: Using PreUpgrade