Jane, some people have had success downloading and installing the new version (18.104.22.168) over the previous version of PAF 5. Others have had all manner of problems. My preference was to move my PAF 5 data out of the PAF 5 program folder. Then uninstall PAF 5 and install the new version. When that was installed I moved my PAF 5 data into this new version's folder.
It is a good idea too, to close down all running programs before commencing the install. Do this by pressing CTRL-ALT-DELETE and clicking END TASK for all items on the menu except EXPLORER (that's Windows by the way) and SYSTRAY. When all are closed down then do the normal Windows install. You should have no problems.