I havent used this plugin yet, but if a folder by the name upload is being created automatically in the bucket then that is the place.
Secondly, there is a configuration by the name TTL under cloudfront. This decides on when cloudfront again goes back to the mapped S3 bucket to fetch new/changed files. You can reduce this to something like 3600 Secs to make it crawl every 1 hour. Then you wait for one hour to see your image come live (if you have published)
If you have made any change to an already existing object (like image, js,css) in S3 then you have to invalidate that object from Cloudfront. Then there will be an immediate propagation of that object to all CDN locations of cloud front.