It's easiest to change the orientation of the picture using your photo software on your computer before you upload it. If you upload a picture onto this website and you click the Preview button, you can edit that or delete it, but you do that in the "your message" box. You can also click the back arrow and you will go back to your original post and can edit. You can also click the finish button, and then go back to your post and click the the word edit on the bottom right side of your post and you can change or delete anything you want even months or years after you make the original post.
I don't use a tablet, so I'm not sure how they work. Maybe others who use can them offer help.
I hope you find this helpful.
