How do I rollback Android 7 Nougat?

S6 Edge vs. Nougat. The color scheme or lack of is utterly stupid. Light gray & light yellow and tiny thin icons. the dictionary is bad, apps have "continuously crashing" even parts of the system apps. My Wi-Fi connection is constantly disconnecting when the signal is perfectly fine. Bluetooth is just as bad. I want to rollback to Marshmallow, how can I do that?. I literally hate my phone now because it's dysfunctional and stupid.