As far as I know:
- You can delete a post by first clicking the three dots next to the reply button at the bottom of your post and then clicking the trash can that appears, at least when you’re a basic user (possibly as new user as well). Some indication of the previous existence of the post will remain, but the content will be gone.
- Deleting a topic that you’ve created (i.e. your post is the first one) is normally not possible directly (anti-spam/abuse). In this case I would suggest either flagging your topic (buttons next to the reply button below your post), explaining that you want the topic removed and why under the option ‘something else’, or directly messaging one of the community moderators.