End a process by name using WMI.

strProcess = "excel.exe"
strComputer = "."

Set objWMIService = GetObject("winmgmts:{impersonationLevel=impersonate}!\" & strComputer & " ootcimv2")

Set colProcessList = objWMIService.ExecQuery _
    ("SELECT * FROM Win32_Process WHERE Name = '" & strProcess & "'")
For Each objProcess in colProcessList
    objProcess.Terminate()
Next