Hi,
qbittorrent-nox is installed via apt packages. Means it will be updated automatically every time you run apt update && apt upgrade, as well on each dietpi-update.
I guess you are still running Debian Buster if qbittorrent-nox version 4.1.5 is installed. This would be the current version on Buster. https://packages.debian.org/search?suite=all&searchon=names&keywords=qbittorrent-nox
To get a different version 4.2.5, you would need to upgrade to Debian Bullseye. https://dietpi.com/blog/?p=811