change my buiss. name in Ma;how do i legally do it?

You may only need to get an Assumed Name Certificate if you're a sole proprietor - if you're a partnership or LC or LLC or Corp you may need the secretary of state to sign off on a resolution. For that you will need a lawyer and probably $600. Sole Props can usually use their SSN as their tax ID. Anything other than that the IRS will need to give you a TIN.

If I'm understanding your original question correctly, you're trying to change the name of your business. How is your name currently registered? Do you have a Tax ID from the IRS, or are you just using your SSN?