While the thread topic and question asked don't exactly correlate.
If you wanna make your file smaller you can go online and type in "online image compresser" through google, upload your file and compress it (depending on how much u compress it the image quality may suffer)
If you wanna upload a picture to the site assuming Ur commenting on someone else's post, hit preview post, upload your picture to a site like tinypic.com, grab the url, search for the upload image button then copy and paste and that should be it.