Setting which render engine is currently active is accomplished by using the Engine drop-down. To change the active render engine, click the button, and choose one of the options listed:
If in the course of exploring an engine, the modifications made to its settings become too confusing, or there is the desire to simply “start over,” use this button to restore the active engine's default settings.
Each render engine is responsible for providing its own advanced settings. Not all engines will necessarily have or necessarily be exposed to any advanced settings. If an engine does provide settings that its developer has deemed “Advanced,” the contents of the Advanced page will change to reflect those settings. As these settings can vary greatly in both purpose and presentation, reference information relating to the settings is located on (or linked from) the render engine's page (see above).