EDIT: So after I wrote this, someone pointed out that you can just update the firmware through the paxx12 firmware-config page at http://<printer-ip>/firmware-config. You can just paste the link for the bin file in there to update. I’ll leave this post as is in case the other info is useful. 

Install Paxx12 Firmware and Enable Remote Screen

I won’t elaborate on this too much since it’s all well documented elsewhere. Here is the doc on how to install it:
https://snapmakeru1-extended-firmware.pages.dev/install

The doc on how to enable ssh access:
https://snapmakeru1-extended-firmware.pages.dev/ssh_access

Enable Remote Screen. Note, I think I needed to reboot the printer, and totally missed that in the instructions the first time:
https://snapmakeru1-extended-firmware.pages.dev/remote_screen

Download the Firmware Via SSH

SSH into the printer. You can use putty to connect to the printer IP. The default username/pass is root/snapmaker. 

Connect your USB flash drive and run the command df -h to find the path to that drive. In my case, it was /mnt/udisk

CD to that directory cd /mnt/udisk but use the path you found above. 

Go to https://github.com/paxx12-snapmaker-u1/SnapmakerU1-Extended-Firmware/releases and copy the link to the latest firmware bin file. Now run the following command to download it:

curl -LO <insert url to the latest firmware bin>

Go to the remote screen at http://<ip of your printer>/screen

Now go to the settings -> About -> Firmwrae Version -> Local Update and click on the firmware you downloaded. The screen will immediately disconnect, but should come back up in a couple minutes.