Is it possible to upgrade the edition?

[HibouValdor]

I think getting the base game is the smartest choice and then upgrading the edition during promotional periods.

[Finwickle]

Yes, at official launch (so tomorrow), but only until the end of the month. The Deluxe content should later still be available separately though, but not the Founders content pack.

See https://civilization.2k.com/civ-vii/faq/

Is there a way to upgrade to the Deluxe Edition?

At launch, you can purchase a Standard to Deluxe Upgrade to receive all content in the Deluxe Edition (except for Early Access, which ends on February 11, 2025). This upgrade option will be available until 2:00 PM PT on February 28, 2025.

Is there a way to upgrade to the Founders Edition?

At launch, you can purchase a Standard to Founders Upgrade or a Deluxe to Founders Upgrade to receive all content in the Founders Edition (except for Early Access, which ends after February 11, 2025). This upgrade option will be available until 2:00 PM PT on February 28, 2025.

Will any content from the Deluxe Content Pack or Founders Content Pack be available for individual purchase?

The Deluxe Content Pack will be available for individual purchase. The Founders Content Pack is available as part of the Sid Meier's Civilization VII Founders Edition, which is available until February 28, 2025.

Content inside each Pack is only available as part of that bundle.