Word has many built-in styles and most likely you are only using a fraction of these. You also can't delete any of the built-in styles.

If you want to clear up the formatting in a specific document, you can do the following:
Copy all the content, minus the final paragraph mark (¶), into a new, blank document.

To show/hide paragraph marks (¶) as well as other nonprinting marks, click the ¶ icon on the Home tab.

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Stefan Blom
Microsoft Word MVP

Microsoft 365 apps for business
Windows 11 Professional