I want to cut the Concrete Slab of 4 inch in my Showroom for bringing Up a new Staircase , hElp mE?

Rent a concrete saw from a local rental company, like A to Z or a hardware store if its big enough. The blade has to be the type used for concrete, and its best if the saw is made for it as well, although you can get an abrasive blade for a 7 1/4 " circular saw and cut about 2.5" of concrete with the saw in the initial stages of the cut. As the blade wears down it cuts less than that. Once you have the 2.5" cut, you can possibly break the slab in chunks along that cut line, but you always have the risk of sending a crack out in an unintended direction. Best to rent the saw that cuts the full 4" depth