Law / If I change my job in Poland without obtaining a new work permit, will this affect my residence visa [21]

Merged:

Changing job -> What is procedure with "karta pobytu" in Poland?

Hi,

I would like to change the job. I work as IT Developer based on "umowa o prace". I've a blue card "karta pobuty" valid till 2021.

Can I just sign a new "umowa o prace" with new employer or will it be required additional steps to be done?

Especially:

1) Should I apply for the new "karta pobuty"? Or I can continue "use" the existing one?
2) Should the employer be able to send documents to local "urząd"? What kind of documents will he need to send in this case?
It will mean that not many companies will want to offer a position...
3) Should I send any notes to local "urząd"?
3) Any other steps that should be done?

Thank you.