Category left undeletable

Hi guys.

I’m new to wp, actually I’m using it since a month ago.

I created a website for our parent’s school association. When playing with categories, I delete one that it seems to be parent of another… now this last category is left undeletable. No matter what I try, I cannot delete it.

How can I do this?.
Do I need to reinstall the theme? Or the site? (I have installed wordpress manually in my domain)

It is not a big deal anyway, since I can rename that category and left it aside and not use it.

I have no content so far.

Thanks for your help!

Enrique