What phone are you using and please clarify your statement as to exactly what is failing.
Sorry, I couldn't add more information yesterday, the forum was acting up.
I have a Droid Razr Maxx HD, I have been trying to do the kitkat update that was released last month.
I am able to download it, but every time i try to install it: it fails. It restarts to the firmware load android, the progress bar goes to about 30% and it stops. Then reboot back up and pops up a message that says "update failed [ok]"
I haven't rooted the device, I don't have any modified apps installed. I have enough space (13GB).