Is it possible to be billed annually instead of monthly?

Yes, and in order to do that you simply refer to the nonprofit approval email you received from us, as it contains links to the discounted upgrades.

Clicking on the Bronze upgrade link would allow you to select the payment schedule, and selecting the yearly plan would switch your account accordingly, with a prorated refund for the remaining time on the monthly Bronze plan you currently have.

I hope this helps. If you need further assistance please let us know. Thank you.