When you are trying to uninstall an App but you are unable to do so as the Uninstall button is greyed out.
The Apps we install requires various permissions but some apps need to be installed with Device Administrator permission. An example app would be the QTrace from Play Store. When you install this app and try to activate, it will ask for your permission to activate as a Device Administrator.
To uninstall an App with Device Administrator Permission, For Most of the Mobile phone's you just need to go Settings –> Security –> Device administrators
Step - 01
Open Setting and scroll down for Security tab.
Step - 02
In Security Tab now scroll down for Device Administrator.
Step - 03
List of Activated App's
Here, you can see the various apps checked for Device Adminstrator access, just uncheck the app that you would like to uninstall and Deactivate it inthe next screen.
Now you can go ahead and uninstall the app normally.