yup this is helps, it took a 2-3 hours but it worked.Guys! I had the exact same problem today. My solution was to keep pressing the "try again" button every time the error appeared on my computer screen. It took some time but the error was appearing at different levels each time in this order : 45% 57% 65% 80% and next the instalation was completed. If it doesn't work try switching to another computer if you can. After the firmware update hits 100% your phone will restart and the LG logo will appear(the led changes its color during this process). At this point you have to just wait a while. Then a dialog box will appear saying that the applications on your phone are configuring themselves. After that your phone will start and work normaly. The cause of the error is the lack of memory on your phone. If those idiots working for LG would say "YOU DON'T HAVE ENOUGH STORING SPACE" this stuff would not happen.
The phone is not rooted!(IMPORTANT)
Phone name: LG G2
Phone model: D802
Old software: 4.4.2 (KitKat)
Actual software: 5.0.2 (Lollipop)
I hope this hellped you solving the problem.
The suggestion worked so well thanksPress and hold the power button till the LG symbol appears, phone will restart.