You can visit http://www.drivehq.com/backup/ to download the latest version DriveHQ Online Backup. Please make sure you install 32-bit version on 32-bit version OS and 64-bit version on 64-bit OS.
If you have already installed an older version, usually, you can simply run the installer to install the newer version, it will uninstall the older version first and then installs the newer version.
In certain cases, if it doesn't automatically uninstall the older version, then you need to manually uninstall the older version, then install the newer version. You can uninstall DriveHQ client software from Control Panel --> Add / Remove Programs.