You must use CustomBild to update DirectAdmin itself. To do this, login to the command line as root and execute the following commands.
cd /usr/local/directadmin/custombuild
./build update
./build versions
./build update_versions
Of course, before that, it is better to run the license system update command once:
update_diradm
Also update the entire server with one of the following commands:
#for CentOS/RHEL
yum update -y
#for Ubuntu/Debian
sudo apt-get update && sudo apt-get upgrade
For more information about directadmin updating visit this: updating software manually