Upgrade from a lifetime plan.
If you upgrade your license from a lifetime plan to another lifetime plan within the first 7 days, you will get a proration discount of your initial payment. After 7 days, you will have to pay in full.
– If you buy a one-website lifetime license for 80$ and after 4 days, you decided to upgrade to a 5-website lifetime license for 120$, you will pay 40$ ( the difference ).
– If you buy a 5-website lifetime license for 120$ and after 10 days, you decided to upgrade to an unlimited-website lifetime license for 230$, you will pay the full 230$.
Upgrade from an annual plan.
If you upgrade from a yearly subscription to a lifetime at any time, you will get a discount based on the unused period of your subscription.
– If you purchase a one-website annual license for 30$ and after 6 months, you decided to upgrade to the same one-website license but the lifetime version which costs 80$. Now, you used the plugin for 6 months (30$/2), that costs you 15$ and you paid 30$, so, you get a 15$ discount.
The entire process of upgrading or downgrading a license is done via Freemius, for more information on how proration works with upgrades and downgrades, read this post on Freemius Docs.