I started cs50 last year (2014) and was not able to finish by years end so I withdrew. Now I'm back with plenty of time to finish. I have the cs5o appliance ver. 19-2 on my computer now. Do I try to load version 2014 over version 19-2, or uninstall version 19-2 for a clean install? I didn't see this covered in the instructions or other posts.
If all your psets were saved in your Dropbox folder, I don't think you have anything to lose by uninstalling the old and doing a clean install of the newest version. Obviously you will want to verify that your Dropbox was synced correctly by going to the Dropbox site and logging in to see that your work was preserved.