you have to enter in the Topic and click in the "Delete" link 🙂

Cheers!

The topic moderation tools (edit, sticky,closed, delete...) are located under the first post of each topic, just open any topic and you'll see them if you're administrator (or permeated to moderated):

Thanks a lot. how can I delete the other members' posts? because they are the technicians. They posted the testing content. Thank you again.

The same delete links are available on all posts, yours and others. You should be admin to see those links and you should be logged in.