Editing your blog posts can have either a positive or negative impact on your search engine rankings.
If you change your images, then make sure that the one your replacing it with is optimized for performance and includes the proper meta data such as the alt tag information for the image.
Images are important for user experience since it increases the potential time on site if it’s visually appealing. But if the image is of low quality, too heavy and doesn’t have the proper meta data, then it can become a negative factor.
Editing your content also has the potential to help or hurt your search engine rankings. You want to make sure that you’re adding value to the article you’re editing. You don’t want to go from say 1,000 words to 500 words. You also want to make sure your article has the right keyword density. Too many keywords and it will look spammy, to little and it might not get the ranking it deserves.
The search engines are getting really good at analyzing content on a web page and with advances in Machine learning, Deep Learning, Algorithms, and artificial intelligence, gaming the system will become virtually impossible. Also, your content will be better understood by the search engines.
I recommend focusing on making sure your first article is a quality article and if you make any edits, they should add value for your readers. Adding value can be in the form of updating information to keep it current and accurate.
Note: you may want to have your edited articles show up higher in your feed so it can get new visitors and go through the process of promoting your new version of your article.