The Galaxy S5, which was released in April 2014, was added by Samsung to the list of smartphones that will be upgraded to Android 6.0 Marshmallow, but the update is expected to roll out in February. If you don’t have patience to wait one more month to receive the latest OS, then you can install the Android 6.0 Marshmallow based on CM13 Nightly ROMs, which was created by CyanogenMod.
If you own the model version G900F LTE of the Galaxy S5, then you can install the Android 6.0 Marshmallow-based CM13 Nightly ROM developed by CyanogenMod, but be careful and follow instructions correctly, if you don’t want to have your smartphone being bricked.
So, the first thing you’ll do before updating your G900F LTE Galaxy S5 to Android 6.0 Marshmallow using CM 13 Nightly ROM is to install the required USB drivers for your smartphone and to enable USB debugging mode, by going to the developer menu. Also, you’ll need a custom recovery tool such as TWRP or CWM, in order to back up your data and to restore it after the update is installed. Also, the battery must have at least 70 percent juice left, so that the installation process won’t be interrupted.
The Android 6.0 Marshmallow-based CM13 Nightly ROM installation file has a size of 286MB and the update comes with features such as Doze (power saver), support for more dialects etc. So, in order to download and install the update, you will start by rebooting the phone into recovery mode (just press and hold down the Volume Up + Home + Power keys until the device’s screen flashes).
Now, perform a backup of your current ROM by selecting Backup and Restore > Backup again. After the backup process is complete, return to the main recovery menu and select wipe data/factory reset and tap in Yes to confirm the action. It will take a few minutes until the data will be wiped and after that, you’ll go back to the CWM recovery menu where you’ll select Wipe Cache Partition and Wipe Dalvik Cache.
You’ll continue by installing zip from SD card, so you’ll locate the CM13 Android 6.0 custom ROM and you’ll press the Power button to select it. You’ll select Yes to confirm the installation and now you’ll wait until the ROM installation process will complete. After the ROM is installed, you’ll install GApps by repeating the above step, then you’ll return to the main recovery menu, where you’ll select reboot system now. After the phone is rebooted, you’ll see that it runs on Android 6.0 Marshmallow-based CM13 Nightly ROM.