Your MacBook Pro comes with two graphics processors, one for better battery life and the other for higher performance. To switch between processors, open System Preferences, click Energy Saver, select “Better battery life” or “Higher performance,” [sic] and then follow the onscreen instructions.
I followed the instructions and opened "System Preferences" -> "Energy Saver". However, there is neither a "Better battery life" nor a "Higher performance" to select.
What could have been the problem?