Fill the foot area of your boot with warm water. Use warm water, not hot water, as hot water can loosen any adhesives used in your shoe.
Allow the shoes to sit with warm water inside them for two to three minutes.
Empty out the water.
Put on a pair of socks. Ideally, they will be the type of socks you intend to wear with those shoes.
Put on the shoes and wear them for the rest of the day. This softens your shoes and helps them conform to the shape of your foot.