New Post: remove an article from the model list

I have from an article more than 1 size available.
There were so many sizes that I decided to move them to a new article with all these sizes displayed as a model.
I took an excisting model and added this to the new article with all these models.
Then I hide the original model.

Now some models are not available anymore (out of stock).
Then the assembly article with all these models does not display this model with the "no stock" flag.
Hmmmm.

So I decided to remove the article with all these models and display theme again all as a separate article.
(back to square 1 :-)
However, when I remove an article from the model list, then there is a recycle icon.
I can not remove the models from the model list.

How to resolve this?