How can I upgrade to a better paying referral system?
That will happen automatically as soon as you buy at least one package of a corresponding type.
By default, all new accounts are set up with the Starter referral package, even if you are yet to buy your first package. As soon as you buy at least one Professional package ($1,000 in btc), your account will automatically be upgraded to the 5-level referral program available under Professional package.
The same rule applies to Expert packages. As soon as you buy at least one Expert package ($5,000 in btc), your account will be upgraded to its referral program that pays commissions up to 10 levels.