click on the reply box at the bottom of the screen. You have to type or put in a smiley etc in the writing area. At the bottm of the reply screen it says additional options. Once that has opened it will say browse, click that it will take you to the picture area of your computer. Type in the name of the file that you want to post, of at least part of it and it should bring it up automatically. Click open, the window will close then click post. If you have any issues lemme know.
WT