I’ve been using AWS facilities for a long time so following along with this guide was mostly trouble free. I did however decide to create a key pair while on step 6 and what isn’t obvious is that the user name for the instance is bitnami, ubuntu works as well. So your ssh session will be started with a command along the lines of:
ssh -i <path to pem> bitnami@<ipaddress of instance>
It is explained on the bitnami/index.html page you get to if you click on the manage icon at the bottom of the start page for the site but I hurried past that the first time.