Catalina, APFS and Disk Utility

Hey all.

I have a string of issues that I'm trying to move through to get Catalina operating. It won't install because the SSD in my mac mini is formatted as Mac OS Extended (Journaled). I have read a bunch of forums so know that I need to reboot in recovery mode, unmount the drive and then select "Convert to APFS". Unfortunately, when I reboot in recovery mode, I seem to get an old Mountain Lion version of Disk Utility which means that option is not there. It's there when go to Disk Utility when normally logged in (I'm running Mojave), but greyed out. I know this is going to be something stupid like I'm holding down the wrong keys when rebooting or something..... But 4 hours in I'm giving up and asking :)