Please note that if you delete the opening message which has received replies, you will delete the whole thread and not just the first message. For this reason, some Forum Owners don't give their members the Permission to delete messages, but most likely give Permission for their members to edit their posts.
For those with the Permission set in place, click the down arrow against Actions at the top of the message.
Click on Delete and then click on GO.
To confirm, click on Delete or click Cancel if you change your mind.
You won't be able to reply in this thread so if you have any questions, please post a message on the Help Forum here or if you are a Diamond Member, you may post in the Diamond Support Forum here. If necessary, I will update the Tutorial, depending on the questions.