I have LR5. Purchased the LR 6 upgrade standalone version. Instead of the upgraded version overwriting LR5 and having one LR application, the download installed a separate LR version on my laptop. I now have LR5 and LR. Was LR5 supposed to be overwritten or am I supposed to uninstall the LR5 application? The images from 5 did get moved into the new version automatically.
If LR6 is working OK you can trash LR5.
Maybe keep your last LR5 backup but usually you won't want to go back again.