Metallic bonding is the answer to your question.
All metals, which have metallic bonding existing in them, are malleable, which means they can be easily change shape without breaking their bonding.
To understand the reason behind this property, we have to know what a metallic bonding is. Metallic bond is the non directional electrostatic force (attraction force) existing between metal cations (atoms but with fewer electrons), and the sea of the delocalised electrons (from the atom itself). Since metallic bond is strong, and the ions are packed regularly, the structure cannot be broken easily.
Once we apply pressure to the metal, the ions adapt a new position and stays in that new shape, thus, we say metals are malleable.