Ok, it looks like you have no room. I was trying to do things the easy way.
Err, one thing to check first:
Are you seeing lots of "mmcblk0p??" or lots of "sda??"
If you are seeing lots of sda?? just tell me and stop for now.
Only if you are seeing lots of mmcblk0p?? can you try this.
Do you have a Type C OTG adapter? Or a Type C flash drive?
Stick your update.zip on a flash drive in the \ directory.
First, fresh fastboot boot rec.img
Wait until the screen goes white.
Code:
# start ttyscreen
# start autoupdate
Then, when it says, plug in your flash drive and cross your fingers.
Keep a camera ready for error messages.