This has been discussed before, notably in bug 2245. There is no way to delete a section (e.g. week or topic) from a Moodle course. There seems to be general agreement that this is A Good Thing, but I can't really see why. I understand the argument that you don't want the teacher deleting a populated section by accident, but you can't even delete an empty section.
The usual workaround is to move the offending section to the bottom of the course page, and reduce the number of sections the course displays. However, bug 4719 indicates the drawbacks in this approach. If a teacher wants to add a new section by increasing this number, the "deleted" block reappears. This is irksome.
If a teacher/editor has powers to delete a resource or activity, shouldn't they have the power to delete an entire section? You are asked for confirmation in cautionary terms every time you attempt to delete a resource, so why not have the same for a section, e.g. "Are you absolutely sure you want to completely delete the section 'foo'?"