The official Android Nougat update is not even out yet for the recent flagship devices like Samsung Galaxy S7 and S6 models. But Samsung Galaxy S4 and S5 owners, who want to taste the Android Nougat flavor, can use a custom ROM to update their devices.
According to Team Android, the 2014 flagship model, the Samsung Galaxy S5, can now be updated with Android 7.0 Nougat through the AOSP ROM. Particularly, it is compatible only with the LTE variant bearing the model number G900F. Talking about the general condition of the AOSPExtended Android 7.1 Nougat custom firmware update, the post noted the following.
"Almost all of the features are working but 1080p video recording is still buggy and very poor otherwise the ROM is quite perfect and runs smooth."
The firmware provides Ambient Display, Battery Optimizations, and Advanced Reboot, among other Android 7.1 Nougat features. However, one should take note that Android 7.1 Substratum Nougat firmware is still in beta stage, which means stability issues and bugs may be experienced while using it.
Samsung does not recommend the use of unofficial and custom firmware to update their devices, as it can cause potentially permanent damage to the units. Thus, every Galaxy S4 and S5 users who will use these custom ROMs based on Android Nougat OS should take more precautions during the update process. Take note as well that installing any unofficial firmware to Samsung Galaxy devices will void any active warranties.
There are also pre-requisites that Samsung Galaxy S4 and S5 users need to follow to ensure that the custom ROM update installation will go smoothly. First, a proper backup of all the important files and settings should be made, in case the update process wipes out the phone's entire memory. Second, the phone should at least have 80 to 85 percent battery power for the installation to push through. Third, custom recovery tools, such as the highly-recommended TWRP and CWM should be installed on the Samsung Galaxy phones to be able to flash the unofficial firmware build successfully.
You can head to the Team Android's posts linked above to learn more about installing custom firmware updates for Samsung Galaxy S4 and S5, as well as access the links for all the necessary download files.