Backup Your Files
If you haven't backed up in awhile use this time to make a proper backup of all of the important files on your device. There's no telling what could happen during/after the installation process so you'll want to make sure everything is safe.
While many of your files are probably backed up into the cloud, you'll still want to ensure that everything is stored properly ahead of your installation. That includes any photos, videos, work/school files, music, and whatever else might be important to you.
To do that, go into your Settings > Backup & Reset to ensure that you are backing up the data on your Galaxy device.
If you need to, you can use Samsung's Smart Switch to move/transfer files and documents around to your other Android devices.
Those could come in handy, particularly for those of you new to Android.