I-140 approved H1b extensions

[mailtsarath]

Hello,

I have a approved I-140 (approved more than 180 days) with my previous employer. I have got my H1 b approval for 3 years (until Sep 2020) with my present employer using the existing I-140. Now, can I apply for H1-b extension without the current employer applying me for Green Card processing? If so how many h1 extensions can I make like that? up to when?

and  can I change my employer right now (new job) without the present employer applying me for GC ?

Regards,

Sarath