What Is The Treatment To Reduce Weight And Get Rid Of Knee Pain?

sir, I do not walk longly because i am facing some inconvenience from back of the knee . I think it is neuro problem but I went a orthopedic doctor ,but he told that my knee water is dried for my over weight ,my weight is 118 kg and age- 40 years , leangth - 6' . so the problem is arise,
I am to much feared , pls tell me about any sollution