Samsung's Galaxy Note 3 was last upgraded to Android Lollipop in 2015, but sadly that's the last official update it will ever get because the device is more than two years old and no more eligible for any software update service.
However, those who are still hanging on to the former flagship phablet can still be able to enjoy Android Marshmallow features on Galaxy Note 3 by installing the custom ROM developed by Dirty Unicorn community.
Prerequisites (Things to remember before installing the custom ROM):
1. This new Dirty Unicorns Android 6.0.1 Marshmallow custom ROM has to be installed on the Samsung Galaxy Note 3 (SM-N9005) LTE model only; if tried on other devices, it might brick them [To check your device model: Go to Settings >> About phone >> model number] Make sure the device is rooted before going forward for custom ROM installation
2. Installation of custom ROM requires clearing of memory in the smartphone, so make sure to back all the data by installing Clockwork Mod (CWM) Recovery/TWRP in the smartphone
3. Make sure the PC has USB driver software, or else the device (Galaxy Note 3) will not be recognised by the computer
4. Make sure the device has more than 80% battery, or else there is chance of the smartphone getting temporarily bricked if the installation process is interrupted midway
5. Though installing custom ROM improve the device's performance and UI experiences, it makes the company warranty void and they will no longer be liable to provide updates in future [users can restore warranty by flashing the device with stock-ROM]
[Disclaimer: This procedure is very technical and should be performed by a person with sound knowledge of rooting (or manual software installation) Android devices. If the step-by-step installation process is not followed properly, there are chances of the smartphone getting bricked or being permanently irreparable. IBTimes India cannot be held responsible for any damage or claims from readers if the procedure does not yield the required results or if the smartphone is bricked. Hence, users are advised to proceed with caution.]
Tutorial: Step-by-step installation procedure of Dirty Unicorns Android 6.0 Marshmallow custom ROM on Samsung Galaxy Note 3 LTE via TWRP (Team Win Recovery Project)-
Step 1: After downloading Dirty Unicorns Android 6.0 Marshmallow custom ROM and Google Apps in to your PC, connect Galaxy Note 3 to it
Step 2: Place the Dirty Unicorns Android 6.0 Marshmallow into the phone's storage memory
[Note: Users are advised to paste the .zip file in the storage root folder, not in any other folder]
Step 3: Turn off device and disconnect it from PC
Step 4: Perform Recovery mode sorties by long pressing Volume (Down) + Power buttons
Step 5: Once entering the TWRP settings menu, clear phone's memory (full) by selecting 'Wipe' option. Once done, select – 'Swipe to Factory Reset' perform factory reset
Step 6: Return to TWRP settings and tap 'Install' by the selecting .Zip file in the phone's memory downloaded from PC
Step 7: Come back to TWRP menu setting to approve the installation by tapping 'Swipe to Confirm Flash'
Step 8: Flashing of the custom ROM begins and after few minutes, a message 'Successful' appears on the screen, thus completing installation
Step 9: If faced with boot loop problem, navigate back to TWRP settings, and select 'Wipe cache/dalvik'. This procedure will help resolve any issue with regard to custom ROM installation.
Dirty Unicorns Android 6.0.1 Marshmallow custom ROM: HERE
Google Apps: HERE
USB driver: HERE
[Credits: Team Android]