Originally Posted by anidel
According to the User Guide that's in the eReader itself, it's possible to remove books from the I'm Reading list by means of their Desktop Application.
Just one of the many mind-boggling flaws with the User Guide. You can't access your "I'm Reading" list from the desktop application.
The only way to alter your "I'm Reading" list is to sign in to your account on the Kobo website. I believe you can remove items from your reading list there, but only items that you've purchased. You have no access to any books on your "I'm Reading" list that are among the 100 pre-installed files.