The invention relates to a system for changing the hammers of a shredder including a shredder with one or more covers and a rotating drum equipped with a plurality of hammers; a lifting system suitable to move said hammers and a control unit which controls both the opening of the shredder and the movements of the lifting system and preferably also the unlocking/locking of the hammers from/on the drum to allow their replacement. The system can be managed hydraulically with a single hydraulic supply. It is included to be able to control the system remotely or to include its automation according to a maintenance plan. A relative method for changing the hammers of a shredder is also disclosed.