There are two reasons you may be unable to delete an app:
1) It is set as a device administrator. Look in Settings > Security and you'll be able to find which apps have been set as device admins. If it's there, unselect it and you will then be able to uninstall it.
2) It's installed to /system. In this case you can only uninstall it if you are rooted, but you may be able to disable it (which has, in practice, the same effect: all data for the app are cleared, all updates are uninstalled, and it cannot run or update and is not using any user storage either).
Of course it may be that it's installed to /system and the manufacturer decided that it's so important they won't let you disable it. In that case all you can do is hide it from the app drawer (if you are using a launcher that allows you to do that) and ignore it, or root in order to remove it (if you think it's that important).