i want to concrete over top of some concrete what the best way off doing it and what the minimum in inch i will get away with with out it cracking please

If the existing concrete is cracking up and moving it probably means that the sub base is poor or non existent so just concreting over the top is not going to be a proper fix and will probably fail in due course.

What is it going to be used for? you might want to consider some reinforcing mesh if it is to be trafficked in which case I wouldn't want to go less than about 4 inches - possibly more depending on the use.

it at a house i rent out, the back yard half of it concret is fine but outher half patchy i was just going to put 2/3 ich over the top to make it look better

What about other options? slabbing may be a cheaper alternative?
Or keep the existing good area, get a man with breaker etc in for a day to break up the rubbish, and use some of that as hardcore. Then lay new concrete level with the existing.
I know removal of "ground" is expensive, but long term it is probably a better way to go. slabbing may be prettier if you think you may sell in the future......

i could break it up myself,thought about slabbing it but though just doing it over top would be easyer

If it is only patchy and not breaking up then if no vehicles are going on it then 2-3 inches will probably be ok.

Good question by the OP, I have been contemplating the same thing with a portion of drive that has little car use, but could be driven on if needed, I may just rip it all up and pave it..

Gravel, chipped slate, etc? By far the cheapest and easiest option and looks much nicer than concrete.