Yep, the old pesky update notification.. I was harassed by it too. For the first time when it popped up, I tried to remove the notification from the notification area by swiping it off but accidentally, tapped on it. Lo and behold, the damn download started but before the download could complete I powered off the phone. That process avoided the update/install altogether. Sneaky LG vs sneaky users..
After when the phone rebooted I got the darn notification again and it lasted me for a good two f*aking days (excuse me for my poetic language).
Now how did it go away is anybody's guess. Am assuming, LG can't possibly push updates to us on a 24/7 and 365 days regime cos their servers will go kaput if they do. Anyway, if LG do go on a mission to harass you.. you can always, stop internet access to the "update centre" by using a firewall. There are many apps and firewalls available on the Google Play store so just take your pick. I'm using Avast (you need to be rooted for that). There is also "No Root Firewall" on the store so... hantam away.
You can also try "Force Stop" from Update Centre by going to -
Settings > Apps > Swipe 3 times from right to left to "All" > Look for "Update Centre" > Click on it > Clear Cache > Force Stop
See if this helps. Personally, I have not tried this as I did not get the chance to go head-on with the abominable update.
Anyway, my suggestion to you is to endure the notifications for 2/3 days and see if it goes away on its own like it did for me.
EDIT:
For those who are rooted, you can easily remove the Update Centre option altogether, from Settings > About Phone by just renaming these 2 files -
/system/priv-app/LGDMSClient/LGDMSClient.apk
/system/priv-apps/LGUpdateCenter/LGUpdateCenter.apk
Example (LGDMSClient.apk to LGDMSClient.apk.bak)
If you ever want Update Centre back just rename them to its original file names. Don't forget after every change do a reboot.
