Unable to update Synology due to insufficient space

Strange message (and misleading message) that says

insufficient system capacity for update” error, you must free up space on the system partition, not your main data storage

I’m pretty sure I have sufficient disk space. Then after some googling, I’ve found out that something else caused the issue. Apparently, there is a “system partition” that has been filled up by some other activities.

I cleaned up this directory, and then the error message disappeared.

/usr/local/lib/node_modules/

Try that, hope it solves your problems too.