“I want to know why they have change the current direction”
As far as I know, Ben Franklin started the convention of marking the electrical flow direction from positive to negative. He actually choose this direction arbritarly. Only after a centuary passed, it was found that the electric current actually flow from negative to positive along with the discovery of electrons. By that time the direction proposed by Franklin became so used to every one and applied in every electrical publications, even in the polarity marking of the batteries and hence it was impossible to change. That is the reason why we still follow his direction convention and we call it conventional direction of current.