A: Hi there! Thanks for reaching out! We asked the AppSumo team about this and this was their response:

Unlike codes, licenses do not need to be stacked, which means you can upgrade/downgrade your tiered plan to your heart’s content. Once the license is activated, you will see the option to upgrade/downgrade it in the Redemption Instructions.

Please note that once a deal has sold out of the AppSumo store you will only see the option to downgrade in your https://share.appsumo.com/C5O as there are no additional licensing tiers available for purchase.

See more information here:
https://help.appsumo.com/article/106-upgrading-downgrading-my-license

Hope this helps!