Cannot Uninstall SEP 12.1.4

I was able to upgrade from Windows 7 to Windows 10 and everything went successfully until recently.  SEP stopped working and will not start.  I have access to SEP by virtue of being a contractor the the Dept of State as well as by being an Adjunct Professor at Northern Virginia Community College.  I have downloaded SEP 12.1.6 but cannot install it because the current SEP version will not uninstall.   I also have access to Norton ConstantGuard by virture of being a customer of Oomcast Internet services.  Until I can successfully uninstall SEP 12.1.4 I am unable to install any anti-virus product.