When creating your category, you can enable "Cumulative packages", this feature allows you to give users discounts based on the packages they bought earlier.
Let's say you have 3 packages on your store;
Rank A: 10 USD
Rank B: 20 USD
Rank C: 30 USD
And the player "example" bought "Rank A", then the next time the player visits your store, he will see the following;
Rank A: Unavailable
20 USD 10 USD
30 USD 20 USD
This way the player can just upgrade their rank, without paying extra for it.