Not sure what you mean about "getting INTO your post." You obviously FOUND the post because you replied to it. If you mean you wish to edit your post, you have to be logged in using the "lockshields" username account and you have to edit your post from the ROOTSWEB side of the boards. Go to any RootsWeb page and click the message board link in the RootsWeb masthead at the top of the page to get to the boards.
The link I gave you takes you an example of a post I posted with an attached photo. When I posted that message with the attachments I clicked the attachments attach file link just below the message box. When you click to browse to find the photo file on your computer there isn't anything about 15 KB...perhaps this is a limitation in your browser? Or maybe your ISP limits the size of uploaded files? You should be able to browse to the file you want to attach and highlight it and click OPEN and that will place the link to the attachments in the box to the right of where it says attachments.