ITSM-NG is stored in /usr/share/itsm-ng and /itsm-ng/var/lib/itsm-ng, you can update itsm-ng folder. If you do so update the version in the control file in DEBIAN folder. Also, update the changelog file to keep track of the changes.
To install the dpkg developper package execute this command:
apt install dpkg-dev
Then, you just need to recomplie it using this command:
dpkg-deb -Zgzip --build itsm-ng
dpkg-name itsm-ng.deb
Note : -Zgzip is only reveleant if you are compiling from ubuntu which use zst as default compression method (debian is not compatible with this compression method)
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