go to http://www.XFree86.org/
There they have links for downloading and readme's and docs explaining how to upgrade.
In Mandrake, I added a 'cooker' mirror source to the rpm package manager, rpmdrake, and it showed me the available rpm packages for XFree86 that were needed to upgrade. Simple.
Since Red Hat is rpm, you could do something like:
$ rpm -qa | grep XFree86
which will show you which XFree86 packages you have installed. Red Hat probably provides the rpm's for the upgrade somewhere. Get the ones that correspond to what is installed on your box, put them in their own directory and, in that directory, do:
$ rpm -Uvh --test *.rpm
If that returns dependency errors, figure out what to do to solve the dependencies. When the command returns to prompt without error, su to root and do
# rpm -Uvh *.rpm
and you are upgraded. You might have to run xconfigurator or some other configuration utility. Look at XFree86.org for instructions. Good luck.