The default size limit for uploading files into OSCAR is 100MB, but you can modify this in the struts-config.xml file:/var/lib/tomcat7/webapps/oscar/WEB-INF/struts-config.xml
The property is set in the following tag, and would need a tomcat restart to take effect:
<controller processorClass="org.apache.struts.tiles.TilesRequestProcessor"> maxFileSize="100M" />