First off you didn't mention what operating system you had. With Windows 8.1 go to control panel look for folder options, select view and select "show hidden files and folders", then click o.k..
Believe for Windows 7 or Vista usually just right click and should be and option for folder options.(sorry been awhile using Win7 i have Win 8.
You can change this back after you decide what needs to be removed, to be able to see all the files on this Drive.
Now if you have used this drive to install software on it, i would be careful what you select to delete, for programs to be on an External Drive there should be a main Programs folder, D:/, E:/, F/: or G/: Program Files (x86) whichever drive letter was assigned.
Another thing is if you are wanting to still use the Drive manager software that comes with this drive and most External Hard Drives, usually to automatically back-up file and folders for you.
I use a External Western Digital hard drive i preferably do not care for the back-up software. You can just use an external drive for backup and not put that software on it, but that is your preference to do it and if you did.
For me i start off with a formatted External Drive and not use any of the back-up software that came with it.
Then i can make any folders and name them whatever i want, Pictures,Music, Documents and Videos(Movies), to keep an order to the files i put in them for easy access.
I was not sure if you do have software on it or not, or just files (pictures,doc.'s)
I would when you figure it out, to be able to clean it well, temporarily move files and folders you want to have on this drive to your main C: Drive, sort things out and delete what you do not care for on the External.
Then format it and put back what you want on it only, go from there in the future.