how to auto update files to S3 bucket when made changes in EC2 instance?

I have a Magento running on EC2 Instance running along with S3 and Cloudfront. I want to know when ever i make changes in any file in EC2 instance which also have a copy in S3 bucket, how can i make it auto update or force update so it can reflect changes in front-end. I know about the Invalidations in Cloudfront. i don't have any idea about update from EC2 instance to S3 bucket.

For example if i make changes to "style.css" in EC2 instance i want to get it updated or force update to S3 bucket and then i can add the file name in Invalidations in Cloudfront to appear in my front-end.

Thanks