spring boot has its configuration file. I guess that you have it included in your jar/war file. So basically unzip that file and look inside it (try to search for application.properties or application.yaml|yml).
property server.port defines the port on which application is running. It defaults to 8080. 
If you are using spring-boot 2 then with property logging.path you can change the path where output file will be placed. However I don't know if this works when you have logback/log4j/... configuration. 
if you run your application you can override those properties specified in appplication.properties|yaml by providing command line properties. For example you can change the port with command java -jar your-boot.jar --server.port=9090