Not all forum areas allow it, but:
Choose Edit, look for a delete button. There will be a radio button that also must be selected. It is not obvious.
The attached image is for the site.
On the iPF app tap the Advanced button at the top right ( while editing ) for the delete option. If it's been a while since I posted I prefer to edit and add an update instead. It prevents confusion if someone has already read and responded to the post.
If you can not edit, you can not delete. At that point you request a Moderator or Admin's help.
Sorry for the delayed edit on this one. I had to swich to the iPF app to upload the image.