1 . By default applicationhost.config file defines following two log file locations. Here IIS_USER_HOME would be expanded as %userprofile%\documents\IISExpress\.
<siteDefaults>
<logFile logFormat="W3C" directory="%IIS_USER_HOME%\Logs" />
<traceFailedRequestsLogging directory="%IIS_USER_HOME%\TraceLogFiles" enabled="true" />
</siteDefaults>
You can update above directory paths to change the log file locations.
2 . If you are running IIS Express from command line, you can use ‘/config’ switch to provide configuration file of your choice. Following link may help you http://learn.iis.net/page.aspx/870/running-iis-express-from-the-command-line/