Best strategy, updating NAS files from attached drive?

Running OMV 6.0.25-1 (Shaitan)

OMV has a file system that needs updating from a portable HDD that I pack in my suitcase. That drive is attached and mounted. I want to overwrite the existing files and directories on the NAS with the files and directories on the portable HDD. IOW, deleting everything on the NAS and copying everything over from the HDD.

I could use ssh command line, or mc, or rsync . . . I'm not sure what is the best way to go about this. OMV ain't straight Linux and I don't want to break anything. How might I go about this?

Thank you.

Thank you. Hold my beer, I'm goin' in!

UPDATE: it worked perfectly. Yay!

I was under the (possibly mistaken) impression that the USB-Backup thing backed up the NAS to the external USB drive, and I needed to do the opposite: overwrite the NAS from the external drive.