OBIEE default port is 9704 to change it ...
Before making any changes backup the files
1. Open the file named default-web-site.xml in OracleBI\oc4j_bi\j2ee\home\config and change the port value
2. Change the port in OracleBI\oc4j_bi\j2ee\home\applications\bioffice\bioffice\WEB-INF\bioffice.xml file
3. Change the port in OracleBI\xmlp\XMLP\Admin\Configuration\xmlp-server-config.xml
4. Change the port in OracleBIData\web\config\instanceconfig.xml
If port is changed to 80 (web port) in Linux only root user can run an application which binds to a port less than 1024.
After the changes restart OC4J