how can i change from married filing jointly to separately without starting over?

Go to:

Personal Info TAB
Find the screen labeled Your Personal Info
Click Edit next to Your Filing Status
Change the status to Married Filing Separate

You will need to remove any of your spouses income and deductions from your file.
    You really should not do that.  It's not just a matter of removing spouse's income, you'
    d have top go back over every single deductions and credit you've entered.  You're much better off starting over.  also, you cannot just change it back to joint again without redoing the entire return.
      Also you can't change if you transferred from last year.  Especially if you want to remove the first and primary taxpayer listed.  It would be better to start over with a new account and username.
        Contribute an answer

        People come to TurboTax AnswerXchange for help and answers—we want to let them know that we're here to listen and share our knowledge. We do that with the style and format of our responses. Here are five guidelines:

        1. Keep it conversational. When answering questions, write like you speak. Imagine you're explaining something to a trusted friend, using simple, everyday language. Avoid jargon and technical terms when possible. When no other word will do, explain technical terms in plain English.
        2. Be clear and state the answer right up front. Ask yourself what specific information the person really needs and then provide it. Stick to the topic and avoid unnecessary details. Break information down into a numbered or bulleted list and highlight the most important details in bold.
        3. Be concise. Aim for no more than two short sentences in a paragraph, and try to keep paragraphs to two lines. A wall of text can look intimidating and many won't read it, so break it up. It's okay to link to other resources for more details, but avoid giving answers that contain little more than a link.
        4. Be a good listener. When people post very general questions, take a second to try to understand what they're really looking for. Then, provide a response that guides them to the best possible outcome.
        5. Be encouraging and positive. Look for ways to eliminate uncertainty by anticipating people's concerns. Make it apparent that we really like helping them achieve positive outcomes.