This article will give the steps to silently uninstall from a machine.

 

Windows Silent Uninstallation

1) Search for cmd in programs.
2) Right-click the cmd icon in the search field.
3) Choose Run as Administrator.  This is necessary for the uninstall to complete.
4) Run the command:

"C:\Program Files (x86)\Backblaze\bzdoinstall.exe" -douninstall -nogui

 

Mac Silent Uninstallation

1) Go to https://secure.backblaze.com/update.htm 
2) Download the Mac installer.
3) Mount the DMG.
4) Open Terminal and run this command:

sudo /Volumes/Backblaze\ Installer/Backblaze\ Uninstaller.app/Contents/MacOS/Backblaze\ Uninstaller

Terminal will request the Admin password for that computer before executing. 

Please note that at this time, a dialog box will still appear asking to confirm uninstallation.