Edit Web.config in Visual Studio .NET

Double-click the Web.config file in Solution Explorer, edit as desired, and save.

Override parent configuration settings

Add a new folder to which the new settings will apply, add a new Web.config file to that folder, edit the Web.config to reflect the desired configuration elements, and save. Add the associated content to the same folder.

Lock down configuration settings

Wrap the settings to be locked down with a <location></location> tag pair with the allowOverride attribute set to False.