To do that you have to create your own JS bundle it is usually in Global.asax or App_Start/BundleConfig.cs
in there you have to add something like below this keep changes according to version so might be little different.
ScriptManager.ScriptResourceMapping.AddDefinition("jquery", new ScriptResourceDefinition
{
Path = "~/Scripts/jquery-" + str + ".min.js", //your path will be ignored
DebugPath = "~/Scripts/jquery-" + str + ".js", //your path will be ignored
**CdnPath = "http://code.jquery.com/jquery.min.js",**
**CdnDebugPath = "http://code.jquery.com/jquery-latest.js"**,
CdnSupportsSecureConnection = true,
LoadSuccessExpression = "window.jQuery"
});
and finally enable cdn in for the script manager
<asp:ScriptManager EnableCdn="True" />
might look little complicate but once you set it will work just fine.