updating

If doing over Wifi - it is very iffy. Much better over Ethernet connection. If not possible suggestion. Shutdown computer and move as close the Router as possible. Disconnect ALL Other devices using Wifi - want the maximum bandwidth only for this computer. Restart the Router first. Restart Computer in Safe Mode - Shift - key immediately at startup. It will do a Repair Disk, clear cache files and only load Apple Software - so loads slowly - Normal. Once Logged into computer - try again.

Has it completely Stopped or just seemed to have paused? Was there and Error message displayed - if so what was the message saying.