September 12th, 2015, 17:00
There's no need to uninstall the 9.1 update - in fact, you shouldn't. It addresses several critical issues that popped up when FS9 was originally released. The process you should follow is to install FS9 from the four CD's, then install the 9.1 update (which requires disk 4 to be inserted), then add in the 9.1 updated version of the no-CD file. After that, you can start installing your other add-ons.
Edit: If you're talking about the link that tgibson posted, that will take you to instructions on removing the Windows Update which disabled the anti-piracy feature that requires disk 4 for the Sim to start.