how to change file names in elements 2018 organizer

I just started using elements 2018 organizer on a new iMac.  I imported a large number of files from an old mac as well as from a card reader reading a camera card.  The camera card files came into Organizer with file names that were the shoot date.  The files that i transferred over from an old mac came now have file names that are numeric and start with 1 to about 100.  I thought that i could just highlight the file and go to file menu and "rename" would allow me to do this, but it is not selectable????  There must be a simple way to do this that i am missing????? Your help is appreciated.  Thanks.