there are two methods you can try.
If you have the administrator account password for the local computer and the best way to uninstall K9 web filter from the local computer is to re-install it! Re-install k9 web protection will simply get you a new license code and a new password you can enter without the need of old password.
1.Open K9 web protection website
2.Click "get K9 NOW" tab on the top-left
3.Fill out the information and your email.
4.Download the K9 Web protection software
from the link included in the email and keep a copy of the license.
5.Grab a version of the K9 web protection installed on your computer, a Google search should do the job.
6.Open "Task Manager" by press (Ctrl+Alt+Delete) and end the process K9filter found in the "Process" tab.
7.Now, you can safely delete the K9 web protection program files. Open computer explorer and go to the folder where K9 is originally installed. It can be found mostly at C:\Program Files/Blue Coat k9 Web Protection.
8.Remove the contents of the folder but not the folder.
9.Run the K9 web protection setup/installer file which has the same version as the one you just delete
10.Provide the license and create your new password
11.Point the installation folder to the same folder you just empty the contents earlier on
12.Now you can have a re-installed K9 web protection with a password you know.
How do you uninstall K9 web protection now? Use the new password you just created
If something goes wrong, install the K9 web protection program downloaded from Step 4.
Reboot Windows into safe mode: restart your computer and hold "F8? key until you see the menu to choose "Safe Mode"
Login to windows and go to "Program Files" directory and delete the K9 folder manually (delete only the contents but leave the folder)
Click "Start"->"Run" and type "msconfig"
Check the tab "Services" and tab "Startup"
Un-check anything that is related to k9
If somehow this method is messed up, try to download K9 again to at least restore your previous installation.
If this still does not work, try to install Revo Uninstaller.
Here is a video tutorial