Every time I select "Check Now" in the System update, it says that my phone is up to date. I assume that I should be able to update to 4.3, no?
4.1 was the last official update the nexus s will get
On 13 November 2012, it was announced that the Nexus S would not be updated to Android 4.2 Jelly Bean. It's still supported by independent developers, though, and Android 4.2.2-based as well as 4.3-based alternative software can be installed. .... Wikipedia