Yifei,
It looks like you are a student in a course wanting to work with Groups. While students can often create groups I don't know that you'll be able to delete one. You'll likely need your instructor to do that. I've include a link below to our help guides specific to students and groups. From there you will find links some items which might help such as how to leave a group and manage a group.
https://community.canvaslms.com/docs/DOC-10701-canvas-student-guide-table-of-contents#jive_content_i...
Rick
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