Haven't filed yet, want to try changing the dependent status but how?

That is under My Info, click Edit by her name and go through the questions.  On your return  or her return?  If you change it on your return it won't affect her return.  You need to change both returns.  What are you trying to change it to?  Did a return get rejected?  

Yes, if you haven't filed yet, you can add, or remove a dependent from your tax return. 

Here's how to remove a dependent in TurboTax Online:

1. Sign in to your return and select  My info.
2. Scroll down until you see your dependent's name.
3. Select the trash can icon to the right to completely remove this dependent.
4. If you want to keep the information in your return, but not claim this dependent this year, click Edit instead. 
5. Continue until you get to Tell us more about (name's) living situation last year.
6. Scroll down to the last question, Did (name) pay for more than half of their living expenses and other support? Change your answer to Yes.