You do that in IIS. If you are using IIS 7, you can add the header in your web.config. It’s in the system.webServer section.
<staticContent>
<clientCache httpExpires="Sun, 29 Mar 2020 00:00:00 GMT" cacheControlMode="UseExpires" />
</staticContent>
This will cause all static content to have an expires HTTP header set to the year 2020. Static content means anything that isn’t served through the ASP.NET engine such as images, script files and styles sheets.
Or to use a relative expiration, use this:
<staticContent>
<clientCache cacheControlMaxAge ="2.00:00:00" cacheControlMode="UseMaxAge" />
</staticContent>
This will cause all static content to have an expires HTTP header set to 2 days.