If you can't remove it with the uninstaller from the installation folder you can try Add or Remove Programs feature:
For Windows XP or bellow you can go to Start > Control Panel > Add or Remove Programs. In the Currently installed programs box, click on the VoipBuster program and then click Remove.
For Windows Vista or above you need to go to Start > Control Panel > Programs > Programs and Features. Select the VoipBuster application and click on Uninstall.
Also if you use a Mac, drag the icon of the program to the Trash.
After that, try running AdwCleaner to make sure that there are no leftover rogue registry keys or toolbars in your system.