I am missing a few grain cells myself;I think they were left in Arkansas. When you click on one of your pictures to enlarge it, the is a bunch of icons on the right side of the screen. Click on the square box with an arrow pointing upwards out of the top right hand corner of the box icon. This opens a box with icons to share on a bunch of social media sites. Just below that row of icons the is a description---small, medium, large, etc followed by numbers, like somenumber X somenumber Following the something X something is an V that is the dropdown that you are looking for. It offers from very small to way too big. The picture I am posting here is Medium 500 X 281 Click on HTML and copy/paste that info and you're done.
I hope I was clear on that, if not let me know and I will try again.