If you’ve installed IE9 over IE8 and for a reason want to uninstall IE9 which appears under installed updates in Programs and Features if you’ve failed to uninstall IE9 then you can use Fix It tool released by Microsoft to remove IE9 from your Computer.
Microsoft Fix it tool to remove IE9
Download and run Fix it tool and follow the steps in the Fix it wizard. If you want to uninstall IE9 that was on other Computer you can save the fix it tool to USB drive and run on the Computer that has problem in uninstalling IE9.
After completion of fix it wizard you’ll be on IE8 version.
Manually uninstalling IE9 using a command
You can manually also remove IE9 by running the following command in the Run command box.
FORFILES /P %WINDIR%\servicing\Packages /M Microsoft-Windows-InternetExplorer-*9.*.mum /c "cmd /c echo Uninstalling package @fname && start /w pkgmgr /up:@fname /norestart"
Read more details here.