Thank you for the help. Unfortunately, I returned the router 2 days ago. I may try again in the future, but for now Linux feels just a bit too complex for me.
It would be great if you could try posting it again. The best 'tutorial' I could find is this from a guy on youtube (that i'm unable to link right now because I don't have permission yet).
It's by Alexander López-Parrado
titled "Windows to Linux / OpenWrt File Xfer + More! Free SFTP, SCP and...