Video bookmarks

A good thing about bookmarks is that everytime that u watch a video, it will mark the watched video, so next day, you will know where the next episode in a TV series to start at.
After watching a complete series of a TV Show, how or is there a easier way to remove all bookmarks from the videos.

Do you actually mean bookmarks because it sounds like your talking about watched status which has an option for changing in the context menu and that can be done on an entire show. If your using an OSMC remote you can also highlight an item in the library and hold down the play button to toggle watched status.