The Galaxy S4 was released approximately three years ago, so Samsung stopped supporting the device with software upgrade. The good news is that the owners of this flagship (the LTE version) are able to install Android 6.0 Marshmallow CM13 custom ROM released by the CyanogenMod community. On the other hand, LG will roll out the official update to its G4, G3, V10 and G Flex 2 flagships.
CyanogenMod Android 6.0 Marshmallow CM13 custom ROM was created for the Galaxy S4 GT-I9505 (jfltexx) international LTE model, so don’t try to install this custom ROM on another model, because you’ll brick your smartphone. So, if you don’t know your device model, you can check it by going to Settings > About phone > model number.
Before starting the installation process, make sure that your phone has been rooted, that memory is cleared and that you’ve backed up your data with Clockwork Mod (CWM) Recovery/ TWRP. You will need to install the USB driver to your computer, because otherwise, the phone will not be recognized. Also, make sure that you have at least 80 percent battery life left, if you don’t want your device to die in the middle of the installation process.
Look on the internet for CyanogenMod Android 6.0 Marshmallow CM13 custom ROM and Google Apps and download them to your PC, then connect your Galaxy S4 (GT-I9505) using a USB cord. The CyanogenMod Android 6.0 Marshmallow custom ROM zip file and Google Apps .zip file must be copied to your phone’s SD card memory, then you will turn of the device and disconnect it from the computer. Now, you’ll enter into Recovery Mode by pressing and holding the Volume (up), Home and Power buttons at the same time. Once you’ve entered the Recovery mode, you will clear the phone memory, and this can be done by selecting wipe data/factory reset.
You will do the same with the cache memory, by selecting wipe cache partition, then you will go back to the ClockworkMod recovery, where you will choose Advanced, and you’ll tap on “wipe dalvik cache”. The next step is to return to the main recovery screen, where you’ll tap “install zip from SD card”. So, after tapping “choose zip from sdcard”, you will go to Android M ROM .zip file from the SD card and start the installation process. The same procedure will be repeated for Google Apps, and after the process installation is complete, go to +++++Go Back+++++ and restart your phone, by selecting the “reboot system now” option. In the end, the installation of CyanogenMod Android 6.0 Marshmallow CM13 custom ROM must be confirmed by going to Settings >> select About phone.
If this method sounds complicated for the Galaxy S4 owners, the good news is that LG is preparing to roll out the official update to four of its flagships: G4, G3, V10 and G Flex 2. The G3 smartphones from Poland were already updated to Android 6.0 and this software is also available for the Sprint G4 Stylus variant which is sold in the US.
When the update will be pushed to your terminal, you will receive a system update message and you will just tap on it and select Download now, then you will manually install the file. The device will automatically reboot itself to finish the installation process. If you want to check if the update is available for your phone, although you haven’t received the notification, then go to Settings > About Phone > Update Center > Check for updates.