I have received EAD and GC was filed. I was promoted and my H1B was amended and got approved by USCIS. Can I change employer and take up position for a different employer. My I-485 is still pending.

The I-485 portion based on AC21 would look at the occupational description as entered on the Labor Certification and not the current H-1B to decide whether the new position is in the same or similar occupational classification. Be guided by your LC/I-140 when making the decision to switch.