Can't speak for Apples (I use a Proper Computer
) but on a PC when you installed Lightroom 5, it should have picked up the catalogues and all other settings from the LR4 that was already installed. If you now uninstall LR4 in the normal way, it will do so but leave everthing that has been used by LR5.
Except it does not delete the LR4 catalog when it's uninstallled. The LR5 installation and catalog upgrade copies the LR4 catalog files and upgrades the copy to LR5, leaving 4's original catalogs intact. Then uninstalling LR4 leaves behind its catalog and deleting it when desired is a manual process. IMHO it's not a bad idea to leave it in place for a little while as a backup until one is sure everything went okay with the conversion. Storage is cheap, so what if you have some tied up for a month or so.