I need to know if sea kelp capsules will give me relief in the water retention in the body specially legs?

No, I dont think it will. In your place, I would visit a doctor to find out if there was any particular reason for the water retention. The doctor may then prescribe diuretic tablets which will help you shed the water. Not sure how bad the problem is, but apples are a natural diuretic and will provide moderate help. If your legs are retaining water, try to put your feet up in the evening so that your ankles are slightly higher than your hips - laying on the sofa with your feet on the arm is ideal.