I presume that you are talking about the update to Android 7. The only way to change it back to Android 6 is to flash the OS. It's an easy process, but it's also very easy to screw it up. You could wind up making your phone into a brick. Before starting that process, you need to learn as much as you can about how and why the process works as it does, and understand the steps required to recover if things go bad. You can find a lot of help for that in the Samsung forums at XDA.
You said that you find that so many actions take so many extra steps compared to what you are used to using. I suspect that most of that will be related to setting things just how you like them. For most things that most folks do, the OS is almost transparent. Once you get your sounds and wallpapers reset, and your homescreen how you like it, most people just don't interact with the OS settings very much.
Often, a lot of issues that come with updating your phone can be fixed with just clearing the system cache and rebooting. You lose nothing with this.
To fix some of the things that you apparently don't like, I'd look at using a theme or even a custom launcher. Your phone came with one or more themes preinstalled, and you can get a bunch more from Samsung's theme store (hit the Galaxy Apps app). Many are free. The great thing about custom launchers is that you can set up your device however you like, including icon spacing, frames, colors and backgrounds, gestures, etc. You can make your device truly your own and have it work precisely how you want. Another neat feature is that you can back up your launcher configuration and restore it after the phone's OS gets updated or even when you switch to a new device. Between themes and my launcher (I switch between Action Launcher 3 and Nova Launcher), the only thing that I can't change from white is the notifications shade. For me, everything else is black. Very easy on the eyes and on the battery.
For your sounds and ringers and other customization, that's likely not an issue specific to this update, but to updates in general. I've had more than my share of phones, and I often lose a sound setting or other customization when I load an update or one of the system apps is replaced. You may have to live with the new BT ringtone. I can't find anywhere to even select a BT ringtone on either my Note 5 or my S7 Edge. If you were able to do that previously, that could be a feature of your particular BT device. Look for an updated app from the BT device maker or check their web site for details.