My 2004 Jeep Grand Cherokee Laredo got a flat tire, and my neighbor tried to jack the vehicle up in my driveway, but it rolled backwards and slammed onto the concrete…
The vehicle is old, and in somewhat poor shape, as such it does not have a working Parking Brake, and there is no available flat surface to work on. I am looking for suggestions to change the tire please, and thanks in advance!!
Call a road side service and have it done . They will have ways to block the wheels .
Block the downhill side of the tire that is diagonally across from the flat tire. Shift the car to neutral to allow the wheel chock to absorb the weight of the car (if it will move at all with the flat). Then change the tire.
CapitalTruck, thank you, but I did manage to get it done, using my jack and ramps!! 
Capital , you completely forgot the part after letting vehicle roll against the chock. The part being - put vehicle back in park if automatic - in 1st or reverse if manual and set parking brake.
Good call!!! Important safety hint! (making an ASS out of U and ME)