Hello I Am A 58 Year Old Woman With Type

Hello I am a 58 year old woman with type 2 diabetes and I need to lose 30 pounds. I have tried other diets, i.e. Dr. Hyman, Weight Watchers and both were difficult to stick to for the long run. I thought I would try old fashioned calorie counting. Can you tell me how many calories I should have per day to lose weight. I also am fairly sedentary (work in an office), so I am planning on starting a walking program along with swimming. I also have two arthritic knees.