Just to double-check, you are going through the "Uninstall" section, right? It shows up just fine on my unit. That said, the previous poster was correct, but if you aren't familiar with command-line work, I'd advise that you learn on something you don't mind breaking once or twice (or at least do your homework first).
There are also other packages that the App Manager doesn't show (system things, libraries, and other things that Joe User doesn't care about), since it abstracts the messy bits away, and those can also be dealt with in the manner mentioned in the previous post - although the warning applies doubly for those.

EDIT: Also as a note, when the previous poster says "appname" in the command, that's not the "marketing" name for the app, but rather the less friendly name of the package it comes in. Usually the names are fairly similar, but don't try to just type in "apt-get remove My Awesome App!!", because that won't work at all.