Buy tools for stretching of shoes in a store. Usually it sprays and foams, which themselves produce shoe brands - Salamander, Ecco, etc. Aerosol spray inside and outside shoes, put on thick socks and walk around the apartment for several hours. Typically, after such manipulations shoes breaks in the leg. If it does not, repeat the procedure until the desired result.
Suddenly, the situation is urgent, and spray for shoes is not at hand? It does not matter. Treat shoes inside castor oil or other fat. Let it soak. Repeat steps again. Significantly softens the skin.
Try to use alcohol or vodka. Apply using fleece alcohol on the skin and immediately put on a very thick socks or stockings. Walk up until the mixture evaporates. Shoes should take several millimeters.
If new shoes or boots too tight heel, then lubricate it with wax, paraffin wax, wet soap, and then gently repel the hammer on the tailpiece. We must act cautiously so as not to damage the skin.
Also, there is another way of stretching the shoe. Pour the water into a plastic bag and place it inside the shoe. Put shoes in the freezer in the morning, remove the shoes from there. During freezing the water expands in volume, thereby stretching the skin.
But you need to remember that soften and stretch can only natural leather. Artificial materials amenable to correction with difficulty.