You can't remove hardcoded subtitles from video files. The term "hardcoded" simply refers to this process. You either blur that area or add a black bar for the entire playback of the video to cover them, thus cropping the video area where things are happening. This is a common practice for people ripping movies in cinemas where hardcoded subtitles are available (mostly in China or Korea).
You can use Adobe Premiere to edit the file and add a black bar, then you can add your own subtitles in the preferred video player or in VideoLan Player go to the Subtitles menu and turn on "Background Opacity" to the highest level. It's the easiest way.