If you added the wrong link, or your photo post didn't work out because of wrong syntax, or if you simply blabbed your virtual mouth too hard, you can edit your post to save face.
Just above the message area for your post, there's a little row of buttons. One looks like a pencil. Click that.

The post edit screen will appear and you can edit, fix, change, whatever you need to do. When you're done, click Submit just as if you were posting for the first time.
Some philosphy on editing posts
If you're editing to "fix" your opinion, it can be slippery. On the one hand, it might be wise to correct data you've learned after the post, however posting something then backpedaling and editing it constantly is kinda weak. You can't delete your post, just edit it, so it will be obvious that you said something and then retracted it. But, it's all up to you.
If someone corrects me in the forum, I take my medicine. Being corrected can be interesting too. It's nice to know the original statement that was in question.
If you're trying to get on a jury, or disavow any knowledge of FAR violations, or you simply stop liking us here at BCP, and you feel the need to have all your posts be gone.... PM me and I can handle that with one click.