Rather than try to make big changes, I would echo the pp recommendation to use My Fitness pal to log everything you are currently eating. Do that for at least 2 weeks, without trying to cut down, and then go back and review.
Identify 1 or 2 things you woud be happy to cut out, cut down or replace.
For example, many moons ago I identified that I was eating a fair amount of chocolate almost every night. It felt like a treat I had a few times a week but the reality was it was almost every night.
I am not willing to cut out chocolate, but I was willing to:
- replace it on week nights with something else to munch in front of the telly. Some really good, sweet dark grapes became my thing.
- replace it on another night with just a few squares of dark chocolate
- cut it down on the remaining night to about 50g worth of milk chocolate, e.g. 1 bar or a small bowl of buttons or similar
Once those first changes have 'stuck' then review their impact on your weight. Still gaining or staying the same? Review again and see what else you are willing to change.
I was then shocked by how many calories I was consuming just in mayonnaise. I love mayo and dislike the low cal stuff, so instead I made efforts to properly measure my mayo serving so that I wasn't just spooning it on.
Make those changes, check weight and review again, if further changes are needed.
Sooner or later you are going to hit a sweet spot, where you have only made changes you are happy to make but have started to see slow weight loss. This way, you discover how to change your weight in ways that you know you can live with - rather than drastic changes you will not be able to keep up for life.
Examples, specific to your OP might be:
- smaller burgers without the buns
- measured portion of chips
- bigger salad but with measured portions of sauce
2 burgers, 160g sweet potato chips, 1 salad and a single portion of full fat mayo would come to around 800kcal. That is perfectly do-able as part of a daily diet. No need to force anyone to eat fish if that's not what they actively enjoy - because you won't be able to do it forever and won't learn any good habits. Instead you will revert back to your preferences sooner or later and the weight will come back.