I don't see a problem with your BMI as long as your weight has been consistent through out the years. If you really want to work out, I suggest going by your body fat percentage rather than body mass index. Also from my experience, dieting is probably the least helpful way to lose weight. If you're just trying to be healthier, try eating PFC balanced meals(like the others have suggested) rather than limiting yourself to calories. Working out & eating right should be something you enjoy so just try to do what you like otherwise you'll just end up giving up on it. The only tip I can give you is to change up your routine. Walking is fine, but don't try to speed walk everyday just because you want to lose weight. Change it up, and try other light/moderate activities once in awhile too !