Changing the Single Event Page URL from stec_event/ to event/
To change Single Event Page URL from stec_event/ to just event/ will have at this point to add few lines of code.
Open your theme functions.php file and on the bottom add this code:
add_option('stec_permalinks', array( 'calendar' => 'stec_calendar', 'event' => 'stec_event', 'cron' => 'stec_cron', ));
Just edit stec_event to just event.
If you get 404 error after that to the following:
Go to Dashboard -> Settings and just click Save Changes without doing anything.
If the problem persist just open a ticket and we will take a look :)