It is mostly about calories in vs calories burned.
Start by reducing feeding quantity 10%. If you free feed, stop now. If you are trying to use the feeding guide on the packaging, USE A 1-CUP MEASURE. Don’t use a coffee cup (12–16oz), or any other type of scoop.
Now increase your dog’s activity. This is good for you both. Go on walks. Go swimming. Play with a laser pointer (watch the eyes!).
Cut out ALL treats. If you really want to give treats… Measure out breakfast and feed that. Immediately measure out dinner, and keep it on the counter all day. All treating comes out of this amount, and whatever is left becomes the evening meal.
If you want to give the occasional green bean, apple slice, etc., reduce the next meal a similar quantity. Some dogs love ice cubes as a treat – zero calories!
Avoid ALL commercial treats, rawhides, bully sticks, pigs’ ears, and so forth. These are packed with calories. It’s like eating healthy yourself, then adding a loaded cheeseburger between meals.
You may need to switch to a diet dog food. Consult your veterinarian about this. There are prescription dog (and cat) foods that are formulated especially for weight loss. These come with professional advice and monitoring.
We all want pets to be a healthy weight. Obesity drives many health problems as pets age.