Now I understand what you meant to ask, and the solution is simple.
When you have double posted by accident, you can choose to not do anything about it at all. It's likely that a staff member will come across your posts sooner or later, and we'll merge the posts. Double posting is not a problem if it doesn't happen often.
You could click EDIT on your second post and copy it, return to your first post and click EDIT on that one too, and then paste the copy into the first post. But it's not worth the effort because you can not get rid of the second post as you're not a Gold member. And it's less work for me to merge two posts than it is for you to edit both of them and move the content from the second post to the first. That's how awesome my power is, lol.
However, if you were a Gold member, you could edit the second post and copy it, return to the first post and paste the copy into there. And then delete the second post.
Gold members also get some cool features, like an extra navigation bar on every page.