2- Save the files on your computer, preferable on desktop.
3- Connect your phone with your PC and transfer the downloaded files on your phone.
4- Unplug the USB cord, power off your Galaxy S4 and enter recovery mode on your Android device.
5- From recovery you have to wipe the system and to clear cache; so
select “wipe data factory reset”, “wipe cache partition” and “wipe
6- Next, load the Android 6.0 M update by selecting “install zip from SD card” followed by “choose zip from SD card”.
7- Apply the last step once more, this time for flashing Google
Apps.When done, go back to main menu of recovery and select “reboot
There you have it; now you can run and test the Android 6.0 Marshmallow CM 13 custom ROM on your own Samsung Galaxy S4. Enjoy.
Credit To Developer