1. Open Firebase Console: Firebase Console.
2. Pick the project where you want to set up Firebase Storage.

1. On the left menu, click Build.
2. Then, from the drop-down, select Storage.

1. At the top of the Firebase Storage section, click the Rules tab.

1. Find the code editor with the current Firebase Storage rules.

2. Replace the existing rules with this code to allow only authenticated users to upload files:

   ```json
   service firebase.storage {
   match /b/{bucket}/o {
   match /{allPaths=**} {
   allow read: if request.auth != null;
   allow write: if request.auth != null;
   }
   }
   }
   ```

3. This rule makes sure that any read or write request to the storage bucket is allowed only if the user is authenticated (request.auth != null).

1. Hit the Publish button to save and apply the new rules.
2. Confirm any prompts to finalize the changes.

1. Use Firebase Authentication to sign in as a user in your app.
2. Try uploading a file to Firebase Storage.
3. Make sure the upload works for authenticated users and fails for non-authenticated users.

By following these steps and setting up the Firebase Storage rules correctly, only authenticated users will be able to upload files.