Each offer has 5 tiers, increasing in contents and price. You can buy 1, 2, 3, 4, 5 or none at all, but you have to buy them in order. Probably best to see them as a package buy.
There are 5 Pricelevels of the offer (A, B, C, D & E) for each region. Which one shows in your game depends on previous purchases. If you would prefer a different Pricelevel you can contact Support and ask for the one that you want. They will happily change your offer for you providing you have not already bought a tier. This page shows all details from Tiered offers.
Use the support button found in the game settings-->choose payments -->change offer price mention the Pricelevel you want in your game.