If you authored a post you can edit it. As well members with a higher level of authorization could edit or even delete the post.
To edit a post you need to be logged in.
You can find the post one of two ways.
You can be in the blog site and you will see an “Edit this entry” link under the post. This only appears if you wrote the post and you are logged in.
You also can in the site admin area select Manage and Posts. Locate the post and select the “edit” link.