If you are going to sell your Galaxy Note 4 or just want to send the phone for repair to the customer service, it is always advisable to remove all your personal data from the phone. This will make sure that no one else can get access to your private data, such as photos or email accounts.
You can manually delete everything from your phone one by one, but the safest and easiest way to do this is just by reseting the phone. When your Factory Reset everything on your device will be wiped out and it will be just like a new phone.
NOTE: Before reset, make sure you backed up all your data, such as photos, videos and other important stuffs from your phone.
After backing up everything, if you are sure that you want to factory reset your Galaxy Note 4, follow these steps.