The good news is you can start with small steps. The easiest is to reduce portion sizes even when you're eating not-so-healthy food. Calories-in-calories-out isn't the only part of the equation, but it is an important part, so just cutting back on calories will help without requiring you to make any drastic changes in the food you're eating or requiring you to cook separately for yourself. This goes for alcohol too, i.e. slowly sipping 1-2 drinks a few times a week vs guzzling 3-4 every other day.
The news you might not want to hear is that it's going to take some discipline on your part. You'll be tempted to get up for seconds when everyone else does or pile the food on your plate but you'll have to make the extra effort not to if you want to keep the pounds off. A trick I like to use is simply eating from a smaller-size plate. It tricks your brain into thinking you ate more, even when you haven't!
1) eat real food - more vegetables, moderate meat, moderate fruits, less grains, less sugar, less vegetable oils.
2) exercise - moderate intensity cardio, sprinting, heavy lifting, dedicated stretching and mobility.
3) live - relax, de-stress, meditate.
Disclaimer: I'm not professionally qualified to make any formal recommendations. I've just done my homework and I'm my own guinea pig. All of my data, unless otherwise cited, comes from a sample size of n=1 (me).