Code:
    With Application
        .ScreenUpdating = False
        .Calculation = xlCalculationManual
        .DisplayStatusBar = False
        .EnableEvents = False
    End With
    
    Dim vSheet As Variant
    vSheet = Sheets("Sheet1").Range("A1:BZ8000")
    
    Dim i As Long, j As Long
    Dim lLength As Long
    Dim lJUB As Long
    lJUB = UBound(vSheet, 2)
    
    For i = 1 To UBound(vSheet, 1)
        For j = 1 To lJUB
            lLength = Len(vSheet(i, j))
            If lLength = 1 Then
                vSheet(i, j) = vbNullString
            ElseIf lLength = 2 Then
                vSheet(i, j) = vbNullString
            End If
        Next j
    Next i
    
    Sheets("Sheet1").Range("A1:BZ8000") = vSheet
    With Application
        .DisplayStatusBar = True
        .EnableEvents = True
        .Calculation = xlCalculationAutomatic
        .ScreenUpdating = True
    End With