download the rpm's you want from kde.org
(you may not want the -devel packages.. and the toys / games packages arnt great)
then drop into runlevel 3.
put all your kde packages into one folder, cd into that folder and
rpm -Uvh *.rpm
then, if u get any failed dependency's, download the needed packages, put em in the same folder, and rpm again.
just the same as upgrading anything else.
just make sure you dont make the mistake all newbs make, and attempt to upgrade a running program.