Have a look in Software Updater | Settings: Any version (instead of LTS versions) Restart Software Updater again.    
Currently, in Software & Updates, it shows [URL] public plus various other similar URLs. My question is will bionic beaver 18.04 show up in the updates as available to install. I saw that [URL] exisits. How do I upgrade using Dell's version instead of the generic Ubuntu 18.04 repositories? Thanks.
XPS 13 9360, Ubuntu 18.04 Upgrade procedure