If you have yet to file your return, you can change your dependent information under:
PERSONAL INFO tab > You & Your Family > scrolling to your dependent(s) and modifying them.
If federal is already e-filed and pending, and you need to add information to or modify your return, you need to wait until it is either approved, or rejected.
If rejected, you can update your return and re-file.
If accepted please see the following regarding amending a return: