Option Explicit

'I presume you've got a lot of file names. 10, 100 or 1000?
'- Start up command prompt (cmd.exe) and run as administrator.
'- Go to directory where your files are. Let's presume C:\temp
'- Type dir /b
'- Look for the little black icon at the top left
'- Choose Edit | Mark. You can now select your files.
'- Choose Edit | Copy
'- Go to Excel and start up a new workbook and select A1
'- Hit Paste

'Now suppose your file name is something like: Fortitude.S01E01.WEB-DL.XviD-FUM.jpg
'and you want to replace the part "WEB-DL.XviD-FUM" with "IMG_" (without quotes.)
'- Go to B1 and enter formula =SUBSTITUTE(A1;"WEB-DL.XviD-FUM.jpg";"IMG_.jpg") Attention, I use semi colon and not comma because I have Dutch version.
'- Copy down
'- Now you have your correct file names in B1
'- Copy and Paste this code in a new module -> Alt+F11 | Insert | Module
'- Run the code with View | Macros |View macros | RenameFiles | Run
'- it will pause and you have to point to the directory where your files are.

Sub RenameFiles()
Dim xDir As String
Dim xFile As String
Dim xRow As Long
    
    With Application.FileDialog(msoFileDialogFolderPicker)
        .AllowMultiSelect = False
        If .Show = -1 Then
            xDir = .SelectedItems(1)
            xFile = Dir(xDir & Application.PathSeparator & "*")
            Do Until xFile = ""
                xRow = 0
                On Error Resume Next
                xRow = Application.Match(xFile, Range("A:A"), 0)
                If xRow > 0 Then Name xDir & Application.PathSeparator & xFile As _
                    xDir & Application.PathSeparator & Cells(xRow, "B").Value
                xFile = Dir
            Loop
        End If
    End With
End Sub