How to downgrade to previous TOAD version?
None. Currently there is no feature in the TOAD un-installation process that will revert a TOAD installation back to it's previous version. If you select uninstall, it will remove TOAD.
You must install a fresh copy of your previous version on TOAD to get it back. For future reference, keep in mind that you can have multiple versions of TOAD installed on your PC. If you know you will want to revert back to a earlier version of TOAD, install the new version on a different directory as a new install and not an upgrade.