0. Charge your device to at least 30%
1. Make a backup with LG Backup Service in settings (ON EXTERNAL SD)
2. Remove SD CARD
3. Download the KDZ for your device: 
H955 here
F510L here, thanks to @Kevin3688
4.1 Download LG UP ( https://mega.nz/#!JtRFkD4Y!u3QgNNaUc...4IZAC57m3rFcsI )
4.2 Download the SD810 drivers ( https://mega.nz/#!VhpDxKoI!Mo0LcQOVO...ApYgpFNMYEl4XU )
5. Install both
6. Connect your phone to your pc (with USB debugging disabled!) and launch the LG UP
7. Select UPGRADE
8. After clicking on the three dots on the right side next to BIN FILE, select the KDZ
9. Click on start
10. Let it cook for a while :
11. profit!