Easier is this (to enable early access):
sed -i 's|builds/RoonServer_linuxx64.tar.bz2|builds/earlyaccess/RoonServer_linuxx64.tar.bz2|' /boot/dietpi/dietpi-software
systemctl stop roonserver
rm -R /opt/roonserver
dietpi-software reinstall 154
Respectively (to disable early access):
sed -i 's|earlyaccess/RoonServer_linuxx64.tar.bz2|RoonServer_linuxx64.tar.bz2|' /boot/dietpi/dietpi-software
systemctl stop roonserver
rm -R /opt/roonserver
dietpi-software reinstall 154
dietpi-software skips downloading and installing the archive, if an instance is installed already, referring to better use the internal updater. Does this actually make any sense? If an internal updater exists, I would prefer using it for updates, as it may do some additional backup or migration steps. However, practically, in all cases I checked, the updaters do nothing different than removing the old instance, installing the new one, and all migration steps are done on first service start after file replacement. So dietpi-software would not do anything different.
In any case, removing the old instance manually enforces dietpi-software to download a new one. This is also printed on the reinstall note, in case the instance is broken and needs to be repaired.
A reinstall won’t touch data and settings in any case. An uninstall indeed purges everything.