Did you try editing your post and reuploading a bit later? That's one option, or you need to learn about peakd. You can start here https://peakd.com/about/faq
Although many social media have a lot of image compression tools built-in, you're less likely to fail if you are able to edit and compress your image file sizes, keeping them less than 100kb works well. Easy enough to do if you have Photoshop or even MS Word. You could also use online compression tools