This documentation is not using the current rendering mechanism and will be deleted by December 31st, 2020. The extension maintainer should switch to the new system. Details on how to use the rendering mechanism can be found here.
Adjust the breaking points via TypoScript to your needs. Default there are 3 images generated (small, medium and large). If you need more breakpoints you can exend the sourceCollection with additional entries.
Additional informations can be found in the TypoScript Reference http://docs.typo3.org/typo3cms/TyposcriptReference/ContentObjects/Image/Index.html#cobj-image-sourcecollection.