I'm not sure why it wouldn't be updating. If you feel comfortable, though, you can always
manually update, downloading them from Essential (the instructions on how to do it are there, as well).
Another option people have used, when their phone isn't showing an update, is to go to Settings > Apps (or Applications) and select show All. Then find Google Services Framework and click the Clear Data button. Then click the Force Stop button. A reboot is likely also a good idea after this; then manually check for updates after the phone has restarted.
Hope this helps.