Maybe an app "froze" the device's operating system and as a result you are unable to remove apps. Restart your mobile device first, and then uninstall the app.
If the app is given administrator privileges, you won't be able to uninstall it until you revoke the privileges. To revoke the privileges, follow the steps below:
Apps that are part of the operating system cannot be uninstalled as they are important to the operating system. If the app you are trying to uninstall is one of them, you won't be able to remove it.
In this case, your only option you have is to turn the app off (or force-stop it) in the Application Manager in Settings:
Select an application from the list -> Tap on Force stop (or Turn off / Disable)
There are third-party apps which may help you unistall unresponsive apps. Some of them include Easy Uninstaller App Uninstall, Fast Uninstaller, All-In-One Toolbox: Cleaner and many more. All you need to do is to install one of these apps, run it and uninstall the troublesome apps.
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