I-140 Approval Copy available, can I change employer now?


I have my i-140 approved and approval copy available with me (EB2). My 6 year completion is Sept 2014 and employer is in process of filing extension.

My question is, if I change my employer after my extension is approved, do I need to apply for new PERM and new I-140 (keeping same priority date of previous employer)?

Or I can use approved I-140 from previous employer and continue my GC processing from thereafter?

Please let me know.