how to change from EB3 to EB2 after I-140 is approved?

Sorry that I cannot type Chinese at this moment.

My case is Eb3, priority date is 5/1/2002. I-140 has been approved. I have not asked for my name-check status because some attorneies say any inquiry will delay the case. Before my priority date becomes current, I'd rather not to bother.

But I have heard people here often saying that it is easy to transfer from EB3 to EB2. I have searched for long time, but haven't found how this works. I really hope to find out. Can anybody help to let me know?

Thank you VERY MUCH!