46f and need to transform

I’m 46 and in a year my brother is getting married. I want to transform myself so I feel confident standing up for him.

5’1”, 180 lbs.

I can follow a diet but drink A LOT and honestly would cut back but not going to stop.

What diet can I follow to lose weight and what beginner (no equipment other than treadmill) workout can I follow to make progress? Not trying to look like a model but would like to lose 20 lbs and firm up. Willing to buy dumbbells, etc.