Start menu - delete a category

The classic Lubuntu menu is overwhelming - too many items.

I understand that system tools/preferences/office categories are needed, but I never need anything from Internet/accessories

How can I delete unneeded category, how can I modify the “start menu” so it fits me?

You didn’t say which Lubuntu version you’re using, but I can say that I tend to use Alacarte for that sort of stuff. It’s fairly intuitive and I’m sure tutorials exist.