You can either use AWS CLI or s3cmd command to rename the files and folders in AWS S3 bucket.
Using S3cmd, use the following syntax to rename a folder,
s3cmd --recursive mv s3://<s3_bucketname>/<old_foldername>/ s3://<s3_bucketname>/<new_folder_name>
Using AWS CLI, use the following syntax to rename a folder,
aws s3 --recursive mv s3://<s3_bucketname>/<old_foldername>/ s3://<s3_bucketname>/<new_folder_name>