The Total Capacity feature was added to the 3.7.2 Hotel Booking version. When purchasing a MotoPress rental theme package (Luviana, for example), you get the inbuilt Hotel Booking plugin. Nevertheless, note that you get Hotel Booking latest version within the theme update.
You should also note that theme updates are released later than updates for Hotel Booking purchased separately. The matter is it takes some time for our developers to include an updated version of the Hotel Booking plugin to each theme. For now, the latest available version of Hotel Booking included to the Luviana package, is 3.7.1.
However, if you do not have time to wait for the theme update to get the latest Hotel Booking version, you can purchase Hotel Booking license, deactivate the inbuilt booking plugin on the website and install & activate Hotel Booking purchased separately (all the data will remain intact). This way you will get plugin updates independently from the theme package.