You can, but
kbxkb,
You can change a job or employer while your I-485 is pending. But there are couple of things you would need to consider.
First, the new job should be the same (or similar one) as the old one on which your I-140 approval is based. Sometimes, not always, USCIS asks for employment verification letter (EVL) before I-485 approval to see if the petitioner is working in the same field as one applied for I-140.
Second, once you start using EAD, your H-1 visa would become invalid. This means that you would be out of status if your I-485 was denied. Of course, the chance of I-485 denial is small, but people suggest that one use H-1 visa or other types of visa as a backup plan for the worst case.
I hope this helps to answer your questions.