How to delete a Collection Type?

I created a collection type in the Strapi admin panel and now I want to delete it, but I don't see an option anywhere in the admin panel to do so. I must be missing something obvious, right?

You can do it in Content Type Builder, steps:

1. Enter Admin panel
2. Content Type Builder
3. Click a collection type
4. Edit (small pen icon next to the name)
5. Delete
6. Confirm

Official docs - Deleting content-types

Another way is to use the admin API, make a DELETE call to:

/content-type-builder/content-types/:uid

To use the API you must have permissions enabled for a role under Roles & Permissions

Endpoints docs

At the time of this update Strapi added a caution (Feb 2022):

Deleting a content-type only deletes what was created and available from the Content-type Builder ... All the data ... is however kept in the database.