I’ve never altered those settings, but the mechanism should be standard among all Ubuntu admin type manuals. One thing you can do is alter when logs are rotated…normally on a system which remains up it would be once per day, and there would be a limit to how many rotated logs are saved…you could set it to rotate every hour and perhaps save fewer or more files (but as I’ve said, I do not know what those particular configuration changes are, I just know they exist and are standard in the Ubuntu distribution).
I believe there is also an alternative mechanism where you can set up your host to receive log information and logging will go over the network from Jetson to host instead of onto the eMMC.
Finally, you could format an SD card or SATA drive as ext4 and mount it at “/var/log” for the mount point…should that run out of space it won’t hurt the rest of the system.