I don't think using yum is feasible for such an early release of Fedora. I seem to remember having trauma upgrading an FC4 system. My best advice is to:
- Download and burn a DVD of the latest version of Fedora.
- Backup any important user files as Faheem suggests.
- Start the installation process (reboot from the DVD).
- At the boot prompt use the 'upgrade' option.
This will attempt to upgrade your system without affecting your user files. If this fails, you'll need to do a fresh installation and re-install your backed up files.
For later versions of Fedora, using yum is much better supported:
yum install preupgrade
This will download the correct versions of all the RPMs required and set everything up so that the system can upgrade itself when it reboots.