Can't delete files on player

At some point in the past I had synced my Clip+ with mediamonkey as well as just dragged and dropped files onto it. The drag and drop files can be found and deleted but I can’t see the synced files in explorer on my computer. I though they might be hidden but changing that folder setting doesn’t do anything. The files can be seen on the device itself as being in a folder “MTP” in the device root. How can I delete them/wipe the player and start again?

Settings->System->USB Mode - switch to MTP mode.  Files copied in MSC mode can only be seen in MSC mode, and likewise for those copied in MTP mode.  Search on this and you’ll find better explanations “why”.

MTP mode is usually needed if you use protected/licensed media (DRM)

MSC mode treats your player as a USB thumb drive (which I prefer), great for drag & drop.

Auto-detect means the device decides which mode (MTP, MSC) it wants to connect with.

Personal recommendation:  avoid the Auto setting, as it can result in some files being MSC-transferred and others MTP, and lead to viewing issues with your computer.  Me, I like good old MSC mode.