Some details, please?
Based on the version number, you seeking to upgrade Safari?
What OS X version?
How are you upgraded or downloading the software? (Directly downloaded, or via Software Update?)
Have you tried quitting all applications, and then performing the Software Update? (Discussion per this thread — but that thread is for iTunes, and I'm guessing you're looking at Safari here?) If that doesn't work, I'd keep everything quit, reboot, and try again.