Find a daily calorie counter and try to eat around 500 kcals below maintenance. If you don’t want to spend the time counting calories all day, just try to eat smaller portions of everything and up the amounts of protein and fats in food while dropping simple carbs like sugars and breads (the crappy plain wheat and white breads, go for multi-grain and stuff). Fruit is still good for carbs. Eat as much veggies as you want pretty much.
If you can’t go running, what about swimming? It’s awesome for cardio. So is biking and they both will put a lot less impact on your knees.
Make more of your meals at home. If there is a dish you like a restaurant, look up some recipes online and attempt them, this will usually cut back on excess sugars and preservatives that fast food and restaurants use, and also help you be more aware of just what ingredients are going into your food which will allow you to make better choices next time you are out. Some of those sandwiches may be delicious, but they may contain 1100 calories vs a regular burger, even with two or three patties containing half that.
Go new places. I think this is the biggest part about getting into diet and exercise is to constantly try out new things. A new workout, a new hobby, a new restaurant… a few years ago I ate hot pockets and played WoW. Now I love all kinds of new hobbies including dancing and cooking (‘bitches’ love them home-made meals) and am in way better shape, along with no more acne or weak immune system or being an anti-social condescending prick.
Sorry for getting a little off-topic haha.