To clear the clipboard go to Edit >Purge > ClipBoard
I am not sure what you mean by delete from your workspace - normally you just close the files.
If you mean the images in the Start workspace then go to File > Open Recent > Clear Recent File list
I do not know why you want to do that... Never felt the need for this. When I exit the application and/or put the next item tio the clipboard, the previous one gone.