You can pay for the current online edition you are using now or you can pay later when you are ready to either e-file or print the tax return.
If you pay now you will not be able to clear the return and start over. But you will still be able to change any tax data you have entered in any section of the TurboTax program. If you pay now you also lock in at the current price. There is usually a price increase in mid-March.
To pay the TurboTax online account fees by credit card, without completing the 2016 return at this time, click on My Account at the top of the online program screen. Then click on Print Center. Then click on Print, save or preview this year's return. On the next page, to pay by credit card, click Pay Now. On the next screen just click on the Continue button. The next screen will ask for all your credit card information so you can pay for the account.