Thanks Michael and Gene. This model (MS310d) doesn't have a built-in server, or ethernet or wifi networking, so that's not an option.
I installed dfu and tried "dfu-util -l" with the printer powered on and plugged in by USB, but it wasn't listed. So I guess it's not supported by dfu. I think I'll just arrange for a friend of mine with a windows laptop to visit and take care of the upgrade.
