You start off by first attempting to Edit the post. If you also have the privilege of Deleting the post - you will then see that option too.
Administrator(s) may decide it's for the greater good of a community, to designate one or more of the sub-forums as no-edit or no-delete zones. There can also be time windows for this, too.
You know Tokyo Jihen is a supergroup, when you can't blame most of the members for wanting to pursue other projects.