If you decide that you need to uninstall one of your systems from Formstack Sync, that is a very simple process. What you will need to do is go to your connectors page in Formstack Sync, click the install button on the connector you want to uninstall, and then choose the account.
That will pull up the connector settings window. Then you will want to click on the more button and choose the uninstall option.
It is important to note that if you uninstall a Connector, Formstack Sync will need to be reset. Please read more here.