You are looking at a US help article. In the Canadian version of TurboTax, you would need to start a new return, and then delete the old one.
To start a new return, select “Start a New Return” from under “My Returns” in the top left corner. Once you have started your new return, you can select “View All Returns” from under “My Accounts & Returns”. Then delete the unwanted return by clicking the small Trash Can next to it or “Delete” under the return’s name.
FYI: There have been changes made to TurboTax Free Online. Please see this TurboTax FAQ for more information: Who can file for free using TurboTax?