How to change Employer (Bangkok)

hi there,
I dont now its correct place to ask or not but , i think may be I can get some suggestions.

do any one know how to change employer in Thailand , I am working in company with holding work permit and Visa sponsor by them, now planning to move new company , this company will offer me assistance for work permit and Visa too but my main worry is that, is my current Non B visa will work for new Employer or I need to go back India and apply for new Non b visa there ?

hope i can get some guideline ,

many Thanks in advance