Replacing a photo on Instagram after posting is not a feature that the platform currently offers. Once a photo is posted, it cannot be directly replaced with a different one. However, there are ways to achieve a similar result.
One option is to delete the original post and upload the new photo as a new post. This will result in the new photo appearing in your profile feed and on your followers’ feeds, but it will have a different caption, comments, and likes than the original post. Additionally, if you had used any specific hashtags on the original post, you will need to include them again in the caption of the new post in order to make it discoverable through those hashtags.