Gregory's ServerI went back to Patreon, found my membership, and they indeed have a way to change your contribution. It was at CA$16.20/year, so I changed it to CA$50.00/year, but it would not accept the change, telling me that the minimum was CA$33.80 (which is $50 - $16.20, but whatever).
I don't think it's a good idea for them to make it difficult for me to give them money.