delete keywords from manager

[BSPicture]

Under Keyword Sets, "wrong" keywords (e.g. with typos, singular instead of plural) are displayed in the manager.

These wrong keywords make it difficult to assign the correct keyword to an image.

How can I permanently remove these unwanted keywords from the manager?

Additional question: It is possible to record a keyword with identical name several times (the names do not differ by spaces at the beginning or at the end). Is this a bug?

[xnview]

you need to delete them from the categories hierarchy panel

[BSPicture]

That's it. Thanks for that.
My workaround was to delete the XnView database, but the method via the category list is easier and more effective