Measure meals, limit extras, and feel for ribs under a light fat cover.

Use a measuring cup instead of free-pouring kibble. Treats should stay under about 10% of daily calories.
You should feel ribs easily without a thick fat layer, and see a waist from above. Ask your vet for a body-condition score.
If weight climbs, increase play first and adjust food with veterinary guidance. Rapid crash diets are risky for some pets.