In order to uninstall the application you can use its uninstaller or Add or Remove Programs feature:
If you use Windows XP or below you can go to Start > Control Panel > Add or Remove Programs. In the Currently installed programs box, click on the AVA Meta4 program and then click Remove.
If you have Windows Vista or above you need to go to Start > Control Panel > Programs > Programs and Features. Select the AVA Meta4 application and click on Uninstall.
If this doesn't work, you can try using Revo Uninstaller. Even if it can't uninstall the application normally, it will force it to uninstall by wiping out all traces of its presence from the system.