OK - thanks

I would need to upgrade to Diamond. The website says "You can upgrade to a higher level (e.g. Diamond) at any time. Simply proceed using one of the contribution options, corresponding to the new level (e.g. Diamond). Your remaining time at the current level (e.g. Platinum) will then be converted and added toward your new membership at the higher tier."

Does that mean, I'm charged just $10 (the difference between Diamond and Platinum) and my expiration date is the same or will I get $45 charge and my expiration gets extended for another six months?