Switching from 'arch' to 'async' redo transport

Hi,

   Some time ago during a busy period we found that the physical standby database was failing to keep up with the primary, even when in 'max performance' mode. We therefore converted to archive log shipping. We would now like to convert this back to max performance protection, with lgwr shipping (async). I was assuming that changing the 'logxptmode' property in the dataguard broker configuration from 'arch' to 'async' would achieve this - but this does not appear to be correct (and database parameter 'log_archive_dest_2'  still includes 'ARCH'). What additional steps do I need to take to revert to log