The script updates most of the services on cpanel system.
First, check if the script exist in the scripts folder: /usr/local/cpanel/scripts/
The file (upcp ) should be under user root / group root and chmod 755
Then go to "Update Preferences" when you are logged into WHM and select below "Operating System Package Updates" the desired option.
Also check root cron file: /var/spool/cron/root and look if something like "...* * * /usr/local/cpanel/scripts/upcp ..." is there.
All cron activity is logged in /var/log/cron (most linux servers). However, if there any errors output from the cron job they should be emailed to the account under which they run.