You can use the TaskManager and right click processes or you can use taskkill /im myprocess.exe /f in the command line or you can use LinqPad.
Open LinqPad, change to C# Statements, paste
var processes = Process.GetProcessesByName("FusionServiceHost").ToList().Dump();
processes.ForEach(p => p.Kill());
and click run. It will kill all msbuild.exe processes. Change the name as you need to.
Process is in the System.Diagnostic.Process namespace.