You would need to create a new return if you just want to prepare your own return separate from your partner/spouse's.

To start a new return, select “Start a New Return” from under “My Returns” in the bottom left corner. Once you have started your new return, you can select “View All Returns” from under “My Returns”. Then delete the unwanted return by clicking the small Trash Can next to it or “Delete” under the return’s name.