"system upgrade" is correct and usable in written English.
It is typically used to refer to the updating of a computer system to make it more efficient or effective. For example: "Our IT department is working on a system upgrade that they hope will increase the speed of our computers."
Removing visible metrics shouldn't be an extension; it should be a system upgrade.
David Fincher has given The Girl With the Dragon Tattoo a very serious software and operating system upgrade.
"The first email with the new format arrived the same day that we had a system upgrade in my office.
A stereo system upgrade can add not only built-in navigation, but also support for smartphone apps.
However, you should obviously make a back-up of your whole hard drive, and any important data, before doing an operating system upgrade.
Jim Kennedy, the White House spokesman, said today that the e-mail messages had been lost in a system upgrade and that some might be recovered.
The bridge was undergoing "an internal system upgrade", the official Xinhua News service quoted officials as saying, but did not specify when it would reopen.
Many people will spend extra money for better-quality merchandise, perhaps in anticipation of a future sound-system upgrade.
Any major operating-system upgrade (whether it's Mac OS X, Windows or Linux) can create incompatibilities with older programs that were written for older systems.
Apple has already said that he'll take the wraps off of Mac OS X 10.5 ("Leopard"), an operating-system upgrade whose significance seems greater because of its proximity to the release of Microsoft's Windows Vista.
Once the codename for Apple Computer's latest operating-system upgrade, the company opted to keep the name because it sounded so cool.
