I recently updated my LR software and now have catalogs named "LR5-2" and also "LR5"; the "-2" version is the new one.
Should I throw away the old one? I have an "LR5.lrdata" folder and a "LR5.previews" folder...Is it best to delete them from inside LR (how?) or to do it in the Finder by just dragging?
You will want to retain the folders that have the "-2" as well. It's safe to delete the older ones, but you might want to make sure you have a backup of the Lightroom 5 catalog just in case you need it in the future. You'll have to delete these files and folders with Lightroom closed. You cannot delete them from within Lightroom.