My MacBook Pro (2011) is saying there are no software updates, however there should be.
For OS updates, the software updater only shows minor releases (so if you are running 10.6, you'll get all the 10.6.x updates etc.). In your case you need to upgrade to a more recent major release (10.8 or 10.9).

I would suggest going into the Mac App Store and examining the new OS X Apple release called Mavericks. It is 10.9 and might have several features of interest to you. Before purchasing and installing it though please backup your computer and files (perhaps via Time Machine).

With 10.9 installed you can run the lastest version of Xcode but be aware, I don't know what other programs you have on your system and it could be that older apps and app versions might not support 10.9 at the moment or without further updating ($$$).