You need to remember which previous antivirus software was installed previously prior to installing avast. On program files/ program files (x86) can you see an antivirus software folder by any chances i.e. Norton, McAfee, or etc. Windows 8.1 might be a bit different from program files/program files (x86). What do you mean by can you run singular uninstaller without causing any problems? That website provided to you list all antivirus removal tool. You just need to pick the previous antivirus removal tool and run it.

What two version of java do you have? The latest version is version 8 Update 45.

Just so you know that I am running Windows 7 SP1 and not Windows 8.1