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 exPressit SE 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 exPressit SE application and click on Uninstall.
Also 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.