New Patio on Old Concrete
 

Good Afternoon, I have not posted here before but as a novice gardener atemmpting my first big project I would really appreciate some advice. I have just moved into a property with an old, cracked and slightly unevenr concrete patio. I want to relay this with flags but am unsure whether I would need to rip up the old patio, screed it level or simply put down a good layer of sand to level it off before laying slabs... Anyone have any hints and tips?