Wrong file - the file for image manager is the .zip file you downloaded and NOT the unzipped file you put on the USB stick
Example - the top line of my image manager after downloading an update - the other lines are previous downloads or backup images generated by image manager.
image_manager.jpg
Don't forget with your v5xxxxx to backup settings menu/setup/vix/backup manager/ press green to backup
You should be able to reinstall these settings after an image manager upgrade (you will get prompt/option to restore at the setup stage of the new update)
Note:backups generated by image/backup manager have the date embedded in the name yyyymmdd