Go to http://www.microsoft.com/getsilverlight/Get-Started/Install/Default.aspx, and download silverlight.exe.
Silent installation from the .exe:
silverlight.exe /q
(doing a silent install from the .exe will also upgrade previous versions without the prior need to uninstall)
If you want to use the .msi, you can extract is by running silverlight.exe /extract. You'll also see a silverlight.7z file, from which you can extract silverlight.msp using WinZip (or your choice of unzipper). You can discard all other files except for the .msi and .msp.
You can then do a silent installation from the .msi, but first uninstall Silverlight 3.0 if it's installed otherwise it'll complain:
start /w msiexec.exe /X{89F4137D-6C26-4A84-BDB8-2E5A4BB71E00} /qn
Then, install 4.0:
start /w msiexec /i silverlight.msi /update Silverlight.msp ALLUSERS=2 /qn /LiV %temp%Silverlight4.log
Silent uninstallation of 4.0 using the .exe:
silverlight /qu
Silent uninstallation of 4.0 using msiexec (same GUID as Silverlight 2.0 and 3.0):
start /w msiexec.exe /X{89F4137D-6C26-4A84-BDB8-2E5A4BB71E00} /qn

I click try again and this message comes up: The path'd: c2d369afb64b silverlight.msi cannot be found. Verify that you have access to this location and try again, or try to find the installation package 'silverlight.msi' in a folder form which you can install the product Microsoft Silverlight. May 14, 2014 Now, I'm getting bugged to install an update through the Microsoft Windows Update web site, but the update is for Silverlight 1.0 and the silverlight.msi file is missing. I can't uninstall Silverlight 1.0 because, again, the silverlight.msi file is missing.

Microsoft Silverlight Msi Download

• 04/21/2010
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Microsoft Silverlight Msi File Missing

• 07/14/2009
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Download Silverlight Msi For Deployment

Microsoft Silverlight Msi