I currently have everything (catalog, image files, previews etc.) on my computer's internal HD which slows my computer down. I have a 1TB WD Passport external HD that I use to back everything up but wondering how I can use it as my primary storage for photos instead of my computer's HD.
I also wanted to mention that right now I have Dropbox sync backup my computer HD, so all Lightroom catalog, image files, previews etc. are backed up there too. Should I change this?
Are you using Lightroom Classic or Lightroom Desktop? They are very different programs. In Classic (or the older no longer supported by Adobe Lightroom 6 and 5 and before that are predecessors), all your files and previews are stored locally on your hard disk. If you want to move the image files to a different drive follow the instructions here: https://www.lightroomqueen.com/move-photos-another-hard-drive-leaving-catalog/
If you are on Lightroom Desktop, all your file originals are stored in the cloud and only transient copies are stored by default on your local hard disk. You can also choose to permanently have a copy of all your images locally if using Lightroom Desktop. To move that you simply point to a different location in the Lightroom Desktop preferences and all the files will get moved for you automatically.
OK thank you. In order to backup the images on Dropbox will I need to manually sync the images and previews w/ the hard drive? Generally confused what I should be making a copy to ensure nothing is lost. Image files, previews, and or other?
Oh I missed that part of your question. What you should do if you want to sync the stuff on the external hard drive is set up the dropbox backup with an extra folder and point it to the folder containing all your images. Your catalog and previews remain on the internal hard disk and should be backed up already in the standard dropbox backup set. (at least I think so)