@Epic_Doors, another non-windows user here, I agree with tut, make a backup of your business files and then try to remove any traces of manager that you have pre-installed.
You could try going through the add/remove programs and making sure they are all removed, that should fix any registry links that may need to be removed as a result of the installer itself, but without ever having used it on a windows box, I’d only be speculating.
I do suspect there are traces of manager that you are going to have to remove manually, @lubos would be the best to to advise, but on a mac and in linux, he created a hidden folder in ~/.local/share/Manager which maintains some information used by manager. Suggested from the following link, it may be AppData\Local\Manager and you’ll need to enable view hidden files.
Hopefully a windows user may be able to jump in and give you a better idea. Good luck