You change your dependency status in the Personal Info section for your name.

If you used the TurboTax online editions to complete and file the 2016 tax return -

Go to this website to download the 2016 amend software - https://turbotax.intuit.com/personal-taxes/cd-download/amend/ty16/

You will need to download the tax data file from the 2016 online account.

When you sign onto to your online account using the exact same user ID you used to create, complete and file the 2016 tax return you will land on the Welcome Home screen.  Click on My TurboTax at the top left of the program screen.  This will take you to the 2016 Timeline.  Under the section Some things you can do:  Click on Download .tax file

Or if you land on the Welcome Back screen click on the blue link Download your .tax file

An amended tax return has to be printed and mailed, it cannot be e-filed.