If i reember right, booting from the ISO's gives you an option to upgrade or install fresh (but yes, have to burn the ISOs).
However, i had mixed experiences doing it on Fedora, when i went 3 - 4 on an install about 6 months old, the update failed and left me with a busted system. When going 4 - 5 it was a fairly new install and it upgraded fine. I guess it depends on how much you have modified it from stock (extra packages, different kernels/modules etc).
I would personally suggest backing up your main configs (yum repos, .bash*, fstab, xorg etc. etc.) and re-installing completely.
I use Arch, which can be upgraded from version to version simply through its packages, no need to reinstall the OS, not sure if the same can be done with FC, just by using the latest RPMS off the CD or via Yum.