I have a USB flash drive that has an iso file of Ubuntu 18.04 on it. To be honest, I don't really remember how I'd done that, might have been with Rufus on Windows, or with the Startup Disk Creator on Ubuntu.
Anyways, can I now simply overwrite the content of the flash drive (I want an iso file of a newer Ubuntu version)? If yes, do I follow the same steps as described here, or are there differences because there is already an iso file on my flash drive. I can currently boot from the flash drive.