current sense switch
How can i reverse the circuit working to trigger the relay when power connected to INPUT and disconnect it when current exceed the set point?


Either -


The circuit has a changeover relay. Wire supply to the common terminal and load to the normally open or normally closed as required.
Swap pins 2 and 3 of U1.



  How can i decrease the minimum current set point from 1A to 500ma or lower?


Adjust PR1 to the correct sensitivity.


  Also i couldn't find IC CA3140 but the seller said CA3130 should work, appreciate it if someone confirm this.


Both seem to run off a 5 V supply, if that's what you're worried about. The CA3130 should work.