It appears these are only warnings, while the overall analysis is a success. I think you can safely ignore these warnings unless you’re not receiving some results you’re expecting in SonarQube.
Upgrading from 7.7 to 7.9.3 is quite easy. Simply download the new software, copy your configuration (sonar.properties) to the new folder, and start up the 7.9.3 instance. Details are here in our upgrade guide.