Do NOT use this tool to DOWNGRADE from v20X to v10X!
You can safely UPGRADE from v10X to v20X or you can upgrade or downgrade between any two versions of v10X and v20X. (i.e. from v10F to v10H or from v20A to v20B)
You can also use LG Mobile Support Tool together with LG PC Suite Version Hacker to install KDZ files.
You can download the tool from the link below:
I myself upgraded from v10F to v10H, from v10H to v20A leaked version and from v20A leaked version to v20A official version using Windows XP without any problems and wihout losing any settings or applications.
Make sure your KDZ file does not contain any spaces in the file name.
I've developed a helper application which can be used to flash any KDZ file on your hard disk using LG PC Suite.
WARNING: Use this application at your own risk.
Here are the steps to flash a KDZ file:
1. Download the application from: http://www.tazetaze.com/?dl_id=5 (186 KB)
2. Extract the LGKDZ.exe file from the zip file and execute it. (Minimum .NET Framework 2.0 required)
3. If you get a warning like the one below, click any button you like. (it does not affect the application)
4. Click "Click to select KDZ file" button and select your KDZ file. Make sure the file name does not contain any spaces.
5. Connect your phone to PC with the USB cable and run LG PC Suite. (tested with LG PC Suite v5.2)
6. After your phone is recognized by LG PC Suite, click the "Upgrade Check" button.
7. You will see the following messages in LGKDZ application and LG PC Suite will tell you that it found a new version. Click the "Upgrade" button and proceed with the upgrade (or downgrade if you chose a KDZ file with lower version)
8. Do not close the LGKDZ application until upgrade is completed.
Waiting for your precious feedbacks...
Note 1: You must have stock LG ROM installed on your phone for LG PC Suite to recognize your phone. With custom ROMs, this solution will not work.
HOW IT WORKS:
When you click the "Upgrade Check" button, LG PC Suite sends a query to LG servers with your IMEI number asking the lastest version of the firmware for your region.
This application captures this request, changes the latest version info to V99Z, and the location of the KDZ file to the file you selected on your hard drive.
So, LG PC Suite thinks that there is a new version, downloads this "new" version from your hard disk, thinking that it's downloading from the LG servers and then flashes the KDZ to your phone.
Translation of this post in other languages:
German Translation 1
German Translation 2