As a master admin of an account, you can choose whether to require your users to upload resources using an upload preset for every upload.
In order to do so, navigate to the Media Library interface. Then, on the left, go to the "Preferences" navigation, scroll down to the "Upload" and click to enable the option to "Require upload preset selection on upload". When selected, a dialog box opens after every upload, requiring the user to select the desired upload preset.
Once the checkbox is enabled, click "save" at the bottom of the page.
The video below shows how to do this: