Source: https://packetpushers.net/ubuntu-extend-your-default-lvm-space/
I didn’t have to follow all that’s in there so to keep it short, use these commands.
Run this first:
lvextend -l +100%FREE /dev/ubuntu-vg/ubuntu-lv
Now, run this second command:
resize2fs /dev/mapper/ubuntu--vg-ubuntu--lv
Done! Refresh your Cloudron dashboard and check stats page. No reboot needed.