Welcome to the forums!
Is there anything special about your phone? Rooted? Unlocked bootloader? Custom Recovery software?
What firmware do you currently have on there?
You could try booting into Recovery mode and clearing the system cache - that'll wipe out the update (in case it got corrupted somehow). Then reboot and try starting the update again.
Sent from my rooted, debloated, deodexed Sinclair ZX-80 running CM -0.001 using Tapatalk