SentryPC will not appear in the 'add/remove program files' folder if you have chosen not to use an uninstaller, so you must manually uninstall it by deleting its program folder where it is installed (specified in the installation section).
Make sure the SentryPC software is NOT running before you try to delete this folder. If SentryPC is active you must login to the control panel using your hotkey and password then shutdown SentryPC. Once it is shutdown and not actively running you can delete its program folder. The default installation locations are listed above, but if you installed to a custom location then you will need to delete that folder instead.
If you have chosen to use an uninstaller then you can remove the software via the Add/Remove Programs control panel or the uninstall link in your start menu.