Upgrade process for CD / Download software

I plan to switch from TaxAct to TurboTax starting this year, 2018.

 

If I purchase a version of the CD / Download software, and discover during my tax preparation that I need a higher priced version, how will the upgrade process work and how will my additional cost be determined?

 

If, for example, I buy the Basic Version early for $39.99, and later decide I need the Deluxe Version. Will I pay the $40.00 difference between the full price of the Deluxe Version and the reduced price I would have paid for ordering the Basic Version early? Or, would I just have to pay the $30.00 price difference between the versions, and retain my $10.00 discount for ordering early.

 

Thanks in advance for any information on past experiences, or if anyone knows what the policy is for upgrades.