Menggunakan CustomBuild 2.0. Jalankan perintah ini:

cd /usr/local/directadmin/custombuild
./build set php1_release 7.4 (ganti angka 7.4 sesuai php yang ingin anda install)
./build update
./build php n
./build rewrite_confs

Referensi: https://help.directadmin.com/item.php?id=345