Is there a way to uninstall an update?

To revert to an earlier release, I suggest you perform a clean uninstall, install while disconnected from the internet, update by applying the appropriate Mondo Patch, and restoring a data file saved prior to updating from the earlier patch release.  If you haven’t already, you may want to review: https://www.quicken.com/support/using-qcleanui-uninstall-quicken. To update Quicken, I recommend you download and apply the appropriate Mondo Patch: https://www.quicken.com/support/patching-updates-windows or http://www.quicknperlwiz.com/quickenpatches.html

To prevent Quicken from applying an update without your approval, I suggest you set Windows UAC settings appropriately (choose default or always notify).