After downloading and installing the update, my macbook restarted. Now its stuck in the blue screen with the round spinning thing. Its been 15 minutes! What should I do?
That's odd. However you could force shutdown the Mac then try and boot up again.
If that does the same then try force shutting down again then hold shift while booting until you see a progress bar along the bottom of the screen. This is a Safe Boot. See if that helps. Reboot again if you get to the login screen to return to normal boot.
Some other thing there is to try, is reset PRAM - I don't know why I suggest this, I just do
PRAM is reset by holding Command-Option-P-R on boot. This causes the Mac to reboot. Let the Mac reboot twice. Keep holding Command-Option-P-R even during reboots.