Here you go
1. Before you start, make sure you backup all your data (If you do not wish to backup your data this step is not necessary) by installing the z4root.1.3.0.apk file onto your phone, then open it and choose 'Permanent Root'. Your phone will root and reboot. Then go to the Market and install 'MyBackup Root', open it and do a backup of your apps and personal data (contacts, sms, call log etc.) Once this is done, go to Settings>SD Card and Phone Storage>Unmount SD Card, a notification in the notification bar should appear saying 'SD Card safe to remove'. Remove the battery cover and remove the SD card and store it in a safe place. Then continue to step 2.
2. Extract the .zip file you downloaded to your computer (e.g. your desktop). Open the folder and install MSXML 4.0 SP3 Parser (msxml.msi).
3. Once that has finished, install LGAndroidDriver_WHQL_ML_Ver1.0_All_Win7.exe which are the drivers so your computer will recognize your phone. Windows XP Users download this driver, extract the contents anywhere (e.g. desktop), right-click on the 'android_usb.inf' file and click 'Install'.
4. Next, open KDZ_FW_UPD.exe
(i) Change 'Type' to '3GQCT' *THIS IS A MUST, THE UPDATE WILL NOT WORK OTHERWISE AND YOU MAY BRICK YOUR PHONE*
(ii) Make sure 'PhoneMode' is set to 'DIAG'
(iii) Browse for the 'V20B_00+Fastboot.kdz' file.
5. Prepare the phone by enabling USB Debugging by going to Settings>Applications>Development>Enable USB Debugging and connect the phone to the computer via USB cable and wait for the drivers to install for the phone. Sometimes the computer still won't recognize the phone, if this is the case, try this: Windows Vista and 7 users press start and type device manager (Windows XP users right click 'My Computer' and click properties, then click the Hardware tab and click Device Manager) then locate LGE Android Platform Modem, right click it and click disable. Accept any warnings that come up. Also, make sure you've disabled Mass Storage Mode on your phone. To do this, go to Settings>Storage>Enable Mass Storage, and untick the box.
6. Click 'Launch software update' and do not use your computer until the update is complete. The update will take roughly 10-20 mins to complete.