Hello,
I saw the screenshots you attached.
1) It is happening because you are having too many items on the menu. Please try reducing the menu items then check back.
2) If you want to change the category icon appearing in the categories menu then you need to Go to >> Products >> Categories >> Edit category >> Icon to display in the main menu.
Screenshot for Clarification: https://ibb.co/HPfgk8h
To remove the category, provide the Url of the website.
Best Regards