Hi,
I am an Indian physician, currently working under H1b research visa (exempt from cap); I am working at Boston and have been offered a residency position (which offers j1 visa only).
1.So, what is the procedure to change from H1b research to J1 clinical visa being in the US? Do I need to file I-539?
2. Do I need any letter/document from the current employer at Boston to get the new visa?
3. If I leave my current job before new J1 is approved, what happens? Am I allowed to stay in the US or should I immediately go back to my home country?

I appreciate your help,

Thanks
SK