You would need to upgrade your rank one at a time until you get to your desired rank. For example, you would pay: Enhanced > VIP VIP > MVP MVP > Executive Executive > CEO CEO > Admin Each rank upgrade costs a little more as you go along, which allows you to have reached a total payment of $105 when you get to the CEO > Admin upgrade.
Also, keep in mind this is not actual Admin. It is a title of a Donator rank named Admin with special perks that regular players do not have. We don't want threads saying, "I don't have /gamemode creative", etc, because Admin is a donor rank, not staff rank (When you purchase it from Buycraft).
As I said, go to the Minetime store, click "Rank Upgrades", and then upgrade your rank one at a time until you reach your desired rank.