Unixmen posted a guide about upgrading from Fedora 12/13 to Fedora 14

This tutorial explains how to upgrade to Fedora14 from Fedora 13 &12. Because your personal data is the most valuable thing in your computer, before to upgrade it is always a good idea to back up any data that you have on your systems. For example, if you are upgrading or creating a dual-boot system, you should back up any data you wish to keep on your hard drive(s). Mistakes do happen and can result in the loss of all of your data.

  How to upgrade to Fedora 14 Laughlin from Fedora 13 & 12