You can either use a third-party app manager or manually uninstall the app from your device's application manager.
For manual deletion, go to Settings > Applications and look for "Apex Launcher". Once you're in the Application Manager, simply hit Force Stop and then tap on "Uninstall". If you're using a third-party app manager, the process for uninstalling Apex Launcher will be slightly different, so be sure to consult that app's documentation.