ITSM-NG is stored in /usr/share/itsm-ng and /itsm-ng/var/lib/itsm-ng, you can update itsm-ng folder.
To install the dpkg developper package execute this command:
apt install dpkg-dev debhelper
Then, set the version in the rules file in debian folder. Also, update the changelog file to keep track of the changes.
Then, you just need to compile it using this command:
dpkg-buildpackage -us -uc -b
Now your debian package is in the ../ folder.
If you also want to update the version, edit the itsm-ng.spec file in SPECS folder.
To compile the rpm you need to follow these instructions :
dnf install -y rpmdevtools git
rpmdev-setuptree
git clone https://github.com/itsmng/packages
cp -r packages/rpm/itsm-ng/* ~/rpmbuild/
rpmbuild -bb ~/rpmbuild/SPECS/itsm-ng.spec