The Android 6.0 firmware for LG G4 was made available today by XDA. The international G4 version got a quick update to 6.0, which means that most H815 models will get the update in due time. Until them you can try your luck with the KDZ files turned into flashables for people with TWRP custom recovery-active phones.
There is no official announcement regarding an Android 6.0 update for LG G4 yet,, but a previously published 20A build shows an early version or a very close to release version available out there. You can try to flash the KDZ file in LG’s Flash Tool or you can flash the files of the system, bootloader, boot partition and the modem through TWRP custom recovery.
If you have an LG G4 that is not model H815 you should not attempt this.
You may want to wait for ann official update as is, because these modifications are sort of dangerous for your phone; there is always a risk of bricking lingering around your device.
Early reports suggest that the build is identical to the older software, at least in terms of design. There are no big changes in the core features or the skin. Official updates for the Asia and Europe international LG G4 versions should be released this week or the next, and the following months should see changes for the rest of the models.