You can easily upload all static files to an object storage of your choice and service it via a CDN. Currently Premium URL Shortener fully integrates direct upload to an object storage such as AWS S3, Digitalocean Spaces and many others.
Step 1 - Setup credentials
You can set up your account and credentials by following the guide for the respective object storage at https://gempixel.com/docs/premium-url-shortener#cdn
Step 2 - Sync existing uploaded contents
Once the setup is done, you can sync all uploaded files directly from the admin panel where you setup your credentials
Step 3 - Upload static assets files
While the sync feature uploads all files uploaded by users, it does not upload static assets. You will need to upload those manually. Login to your hosting control panel or FTP to your server. Go to /public/ folder and compress the "static" folder. Download and upload all files in the static folder to the object storage storage of your choice. Once that is done, go to the file config.php and you will see the following line:
Replace null by a the url to the static folder - make sure to add the static folder at the end e.g. https://mycdnendpoint/static
Now all of your files will be served via the CDN. New uploaded files will be automatically uploaded to the object storage and served via the CDN.