Hi @aram_coulter,
Unfortunately you cannot downgrade after starting or upgrading to a particular product. If the upgrade was due to your tax situation you will need to keep the upgrade in order to file. If the upgrade was in error unfortunately you'd need to restart your return. You can also contact our support team for additional assistance:
https://turbotax.community.intuit.ca/turbotax-support/en-ca/help-article/tax-return/contact-us/L1h8P3E0x_CA_en_CA