You can manage your data usage and download quality from the Data Settings page in the Showmax app.
Data usage
By default, downloads occur only when connected to WiFi.
You can allow downloads via mobile data by switching the toggle in Data Settings in the Showmax app.
Download quality
By default, downloads occur at up to 160 MB/h.
You can change this to an option which suits your data plan, by selecting from the options in Data Settings in the Showmax app.