how do turn off "mode attribute" in web.config. configuration file

[hbbauer2]

To enable the details of this specific error message to be viewable on remote machines, please create a <customErrors > tag within a "web.config " configuration file located in the root directory of the current web application. This <customErrors > tag should then have its "mode" attribute set to "Off".

<!-- Web.Config Configuration File -->

<configuratio n>
<system.web>
<customErrors mode="Off"/>
</system.web>
</configuration>

How do I do this?