If you are running php 5.4 on the server and want it to be upgraded to 5.6 . Additionally, your server has custombuild 2.0 installed then you just need to follow the below steps for the upgrade -
custombuild 2.0
cd /usr/local/directadmin/custombuild
./build set php1_release 5.6
./build update
./build php n
./build rewrite_confs
That's it!
./build set php1_release 5.6
./build update
./build php n
./build rewrite_confs
That's it!