Fikicoins are basically a currency. Sevenops is going to be making a google form/app where you'll be able to "buy" a new username soon.
Your first username change is actually free, so there's no need to worry about the fikicoins as of right now.
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EDITED:
These are the prices:
3 fikicoin = 12.99$/€ - 15.47 USD
1 fikicoin = 4.99$/€ - 5.95 USD
Question answered, thread closed.