Debian is able to upgrade to a new version but it is not an easy task for the upgrade procedure. It has to decide how to upgrade options you have modified and/or set. If it doesn't know it will ask you what to do. Usually it will present the old configuration as default but it may not be always the best decision. This also implies that you will not get exactly the same installation than from a new installation of the new version. But the result is mostly very good. But you may miss new features from the new version because it tries to use the old configuration as already said.
You should clone your current installation on a spare SD Card and do the upgrade. If it doesn't show the expected result you can try again. When you have changed the settings in /etc/apt/
to the new repositories then the commands to upgrade are:
rpi ~$ sudo apt update
rpi ~$ sudo apt full-upgrade