Back up your Haveno data directory first through Account > Backup. To be on the safe side be sure you properly backed up your wallet seed.
See https://docs.haveno.exchange/haveno-ui/backup_and_restore/
If you are using the AppImage, it should work to download the newest version and replace the existing one.
If you are using the Deb package, it should work to install the newest version just like you installed the previous version (command line: dpkg --install package.deb).
I'm not sure if it's the OP case, but I bet that some those questions are referring to the installation in Tails (which is not through a .dec but a .zip according the guide)