Subtitle Sub Track entries - How To Remove

[koitaki]

How are subtitle files removed so that they don't appear in the Subtitles, Sub Track menu?

I've been messing around trying to get an .ass files to work, and I've now got about 10 subtitle files appearing in the dropdown menu.
I'd like to get rid of them all, but haven't yet found a way to do this.

Thanks in advance
(Windows OS)