Lowering Cholesterol and reducing strain on liver?

My partner has been steadily gaining weight over the past three years and has gone up by two stone. However, he has a pretty limited diet and he’s so fussy it’s painful.

Recently he had a blood test that showed his bad cholesterol was very high and his liver was sending out distress signals.
Is there any way to bring the cholesterol down and reduce strain on his liver? He’s a sucker for fizzy drinks, chocolate and bread and most days that’s all he will eat. I’m at my whits end a bit here because I want him to be safe and eat a more balanced diet.

Any advice?