In recent theme versions the sermons were extracted into a separate plugin due to popular demand.
To change sermon to some other slug, please follow the instruction below:
1. You need to edit wp-content/plugins/vamtam-sermons/vamtam-sermons.php. You need to modify the "labels" on lines 50-62 and 87-100. You will also need to change the names of the two widgets. Edit both files in vamtam-sermons/widgets/ - the strings that you have to change are in the __construct() functions.
2. Change line 70 in wp-content/plugins/vamtam-sermons/vamtam-sermons.php. Add an identical rewrite array element to the call to register_taxonomy below (refer to the documentation here:https://codex.wordpress.org/Function_Reference/register_taxonomy)
You might also need to flush the rewrites cache. You can do this by switching the permalinks to "default", saving, then changing them back to whatever they were.
In the event where we release an update of the plugin you will need to do this again. Make sure that you've backed up your changes before updating the plugin.