Although folder names are shown separately in the Media Library, when your files are stored in your account, the folder name is part of each file's identifier / public_id and part of the URL used to access each image.
As a result, there isn't a simple 'rename folder' operation, but instead, the equivalent operation is to move the files to a new folder with the desired name you need, which will effectively change the folder name from your perspective, and also in the URLs to access the files.
You can do this using our API, using the Admin API to fetch a list of the existing images, and then the rename method for each file, replacing the old folder name with the new one: https://cloudinary.com/documentation/image_upload_api_reference?query=rename&c_query=Rename%20method#rename_method
The following article explains how to rename a folder that already contains resources.
If there are a few affected files, you can do this in the Media Library by selecting them and moving them to the 'new' folder.