If you directly installed 2.0.3.7 through an installer, then that is now your “base version” which is as far back as you can downgrade without “over-installing” from an older installer. You can check your base version by looking at the BaseVersionName line on the main “About” → “System info” page.
If you updated to 2.0.3.7 using the GUI updater, then you should be able to downgrade using the steps described here: