Information from the past year and carry-forwards may have been transferred into this year's return from your self-employment entries. If you wish to downgrade, you will need to start over from the start and not transfer last year's return because once the return is upgraded it is not possible to downgrade.
If there are donations in box 46 of a T4 or Employee-paid premiums (medical) in box 85 of a T4 which would require an upgrade to allow you to claim additional credits not included in the free version, this may cause an upgrade. Please see the list below enumerating what is or is not included in the free version.
One of the nice things about turbo tax, is NOT having to start from scratch and enter everything (name, sin, address, last years amount$, etc.). To me, that's a flaw in your system, that it assumes you're self employed now, because the previous year you were. I understand the answer of start a new return from scratch, but that is not a customer service user friendly answer.