How to change the key value present in web config dynamically

Suppose there is a key present in web config and which have the value 10.

Example:

<add key="Unit" value="10" />

You can modify the value programmatically using this code

Code Behind :

Configuration webConfigApp = WebConfigurationManager.OpenWebConfiguration("~");

webConfigApp.AppSettings.Settings["Unit"].Value = "15";

webConfigApp.Save();

Namespace Required:

using System.Configuration;

using System.Web.Configuration;