Go to Control Panel - Program & Features and see how many times Manager is listed.
If only one, then via Control Panel uninstall Manager, then go to the Manager programme file location - users/(user name)/appdata/roaming - and make sure the folder is empty, in fact you could delete the folder. Shut down, wait a few minutes and start (not just a restart) the computer and start download as a clean (new) install.
The Manager data files location (unless you have relocated) - users/(user name)/appdata/local - should be unaffected by the uninstall - however either do backups (if you can) or copy the Manager data files folder on to storage device as additional protection.
PS: if you need to copy the Manager data files back, only copy files that are missing from the data folder.