Update to 64-bit 12.04LTS fails. I remade the LiveUSB once using Startup Disk Creator, and twice using unetbootin. I then, thinking it was the USB, used a different one using unetbootin. Also a failure. I have an HP 2000-2d69NR Notebook PC, 1.75GHz AMD E2-2000 CPU, 4GB RAM, AMD Radeon HD 7340 Discrete-Class graphics, 500GB HDD with Ubuntu 12.04LTS amd.
From what I understand, you can't boot into the live CD, right?
In your bios, try to disable UEFI boot, and set it to Legacy mode. Disable safe booting, too. Also, make sure that USB is at the top of the boot list, I always forget that :)
If you mean that the update starts, but fails, you would need to provide provide more information on your problem, your question is a little unclear :(