How to remove styles from Normal.dotm

You can turn on the "Hide until used" or "Hide Always" in the Manage Styles dialog that Jay showed. They are found in the "Recommend" tab.

https://office-watch.com/2016/word-where-are-all-the-style-controls/

You also have the option of setting the  "Set priority to use when sorting in recommended order" value to "Make Last" for those styles. That way they will be so far down on the display list that you probably won't see them. 

Personally I prefer to use the "Alphabetical" sort order. I found that managing the recommendations was too much work. But you may have to use them.

You cannot delete any built-in styles (which include all the Heading N styles) from any template or document. However, you can prevent specific ones from appearing in the Styles gallery.

In the Manage Styles dialog that you showed, or in the Styles gallery or the Styles task pane, click the Modify button or the Modify item on the right-click menu. In the Modify Style dialog, clear the check box for "Add to the Styles gallery" and click the option button for "New documents based on this template".

Repeat for each of the styles you want to suppress. Remember to save the Normal.dotm template if you're prompted when you shut down Word.

Glad to be of help.

Correct, changes to your NORMAL.DOTM will not affect existing documents. But if you have several styles that have been changed, you can use the "Organizer" to copy those styles from your NORMAL.DOTM into the document.  It is much faster than manually applying changes to each style in each document and is more consistent. You don't accidentally forget an element.

Introducing the Organizerhttp://wordribbon.tips.net/T005972_Introducing_the_Organizer.html

Using the Organizer to Manage Styleshttp://word.tips.net/T001351_Using_the_Organizer_to_Manage_Styles.html

As you work with a document or a template, the number of styles you use can grow rapidly. At some time you may want to delete styles, rename them, or copy them from a one template or document to another. The easiest way to perform these tasks is by using the Organizer.

although this article was written for the menu version, it is still mostly applicable to the ribbon versions.

Thanks Rohn, that's great for Normal.dotm and all files that are created from it. I have set Headings 7-9 to be always hidden. Of course it does not affect documents created from Normal.dotm prior to today - I guess it would be too much to hope that it could affect all such documents. But at least a great step forward. Your and Jay's assistance in this are much appreciated.

Many thanks Jay - that looks to be exactly what I need. But for some reason I cannot make it work. I have made the change both in Normal.dotm and a new document based on it, but the recalcitrant styles still appear in the style gallery and in the pull down style list.

So not sure what is the problem. My styles do not have the (hide until used) against them. Is this an issue? How would I switch it on?