You will only be charged a pro-rated amount for days left before your plan's re-cycle date.
You will be charged immediately for the difference in pricing.
Please note: if upgrading to a yearly plan you will be charged the full amount. There will be no refunds for annual plans.
Once the limit is reached, you will be automatically upgraded to the next pricing tier. You can opt-out of this feature in the account settings. If you do opt-out, scheduled pending emails will sit in queue and will send out once your plan re-cycles or you upgrade.