If you have an I-485 pending for more than 6 months (which it would appear you do not), and you switch employers now, your new employer will have to start a new case for you. You will get to use the priority date from your old case, but you will still need a new case. If your priority date is current, you should consider filing the I-485, waiting six months, and then port to a new employer, in which case you would not need a new I-140. If your PD is not current, then, depending on how long you think it will before your PD becomes current, and how badly you want to move, you may want to go ahead and move. You will, however, need to do an H-1B transfer to the new employer.
You indicated that it was just approved. You may switch jobs (and will probably need a new H1B since you do not have a work card) You will need to start all over with the new employer on an I-140 filing. I agree with my colleague above about the priority date.
Under the guidelines set by AVVO, this response is general information only and not specific legal advice, and no attorney client relationship is formed by this response to your question.