I believe that the forum software supports standard users being able to delete their own posts but I think it's disabled by design.

Although you could be empowered to delete individual thread posts, others might have quoted your post, so that needs manual tidy up, and that needs moderation privs.

Deleting a specific reply on a thread does cause issues with numbering of posts on threads, this is more of an annoyance than an issue.

Where someone wants to delete the first post in a thread topic - do they have the power to unilaterally consign all discussion that ensued to the bin? That may annoy others who loose their contributions.

So I think for the above reasons the feature is disabled. You can of course just edit your post to remove the content and just say you deleted it. The process at the moment is to hit the ! Symbol on your own posting and explain to moderator what you suggest is done and why.