I’m trying to only purchase the Plus Upgrade so I can access past tax returns and documents. The program keeps only letting me upgrade to Deluxe which I do not need.

[Critter]

Click on Upgrade Now (if Plus is grayed out then you are already using Plus and only need to pay for the upgrade)

To pay the TurboTax online account fees by credit card so you can access your prior year online tax returns, click on Tax Tools on the left side 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 show a review of your Fees, click on Continue.  Complete the next screen to pay by credit card and click Continue.