When you are posting......... scroll down to bottom to additional options...there you will find Manage Attachments. Follow steps. It's pretty easy.
If your pics are too big and need to be resized you can either do it through your photo program or use an online image host. I use Photobucket. It's easy and quick. You download your pics, chose edit at the top of pics you want to resize, and chose a size. I use website and have never had an issue. Then just upload it to this site through the manage attachments.