Hey, XCOM, no problem. I looked you up, and you're currently at the Game Tier ($15). To bump up to Beta Tier ($35 total) or Alpha Tier ($50 total), you'd be looking at a $20 or $35 difference, respectively. As I mentioned, you can send the difference to firstname.lastname@example.org via PayPal, including a note with your email address and what tier you're upgrading to.
Whether or not you decide to upgrade, we really appreciate your support. Hope you've enjoyed the game!