There is no update to Elements 2018. You can only upgrade to a higher version. The current version is Elements 2020 (which is actually version 18). Where did you get the idea that there is an update to Elements 2018?
There may have been an update to the Adobe Camera Raw plug-in that came with Elements 2018. I don't currently have that version on my machine so can't check, but my vague recollection is that there was not. If there was such an update, you would find it by going to the Help>Updates menu.