Make sure that the user account you use to authenticate the update installer is an administrator account.Restart your computer and try installing the update again.If it is at another location on your computer, move it to the Applications folder on your startup volume, and then try installing the update again. Make sure that the Microsoft Office 2008 folder is located in the Applications folder on the startup volume.
This step might have been performed for you.
4.9 (Tiger) or a later version of Mac OS Note To verify that your computer meets these minimum requirements, on the Apple menu, click About This Mac.
Supported Operating System Apple Macintosh, Mac OS X There is no upgrade from Office 2008 H&S to Business edition. Microsoft Office 2008 for Mac Home and Student $43.07 (does not not contain Exchange support) Microsoft Office 2008 Business Edition upgrade. Office 2016 for Mac is a available now as Office365 subscription. Office 2016 brings welcome uniformity by making the Mac version nearly identical to the Windows version. Office 2016 is a much welcome upgrade for any existing Office installation, particularly for Mac users who’ve been suffering under the rather awful Office 2011 with its ugly, clunky interface.