Several causes. Stinky feet may be due to excessive perspiration or some type of infection. Try to keep the foot dry by using a powder or antfungal spray and good hygeine. If this does not help you need to seek out professional help to determine the cause.
Hyperhidrosis. Feet have more sweat glands than any other part of the body, so they can sweat profusely which can not evaporate (like it can on the hands) due to being enclosed in footwear. The foot bacteria produce isovaleric acid which is what causes the odor. Treatment can be otc certain dri, prescription drysol, iontophoresis, botox, oral medication, and topical antiperspirants.
Answer. Buys new shoes. Always wear socks and change twice a day. Don't wear sandals/flip-flops.