Eat clean and exercise daily
Simplest cleanse is fasting, but cleansing what? There are liver cleanses, colon cleanses, kidney cleanses -- they can be very good for health, but not very useful for losing weight in a healthy fashion because the weight will just come back as soon as you return to your normal way of eating. The only way to lose weight long-term is to change your metabolism, which doesn't involve calories as much as it involves what you eat and how quickly it turns into sugar and how easily it moves through your digestive system. So if you want to cleanse for health purposes, what part of the body, and if you want to cleanse for dieting, not a great idea.
A simple pitch of water with slices of lemons, limes, and cucumber can be a cleanse that's natural and not harsh. It helps with excess water.
You don't need a cleanse! You need to count calories and exercise!