There is no way to make an actual shoe smaller. However, one can make a shoe feel smaller by adding products that fill the shoe, leaving less room for the foot. Traditionally, when one wanted to make their shoes smaller, they would simply ball up a pair of old socks into the toe of the shoe.
People who want their shoes to fit more tightly can use a cushy insole. When people think of insoles, they typically think of large bulky shoes, but Sexy Soles, for example, are designed to fit inside heels and stilettos. If someone's heel is slipping out of their shoe, they can make that part of the shoe smaller by putting band aids or rub relief strips on the inner heel of the shoe. Another way to make a shoe feel smaller is to tighten its laces.
Rather than trying to change the size of their shoes, some people get plastic surgery on their feet. Depending on the surgery, this can make a shoe that is too large fit more tightly. According to the UK Daily Mail, people get their toes lengthened, and they get their feet padded through Botox injections into the pads of their feet.