Substitute code partly working

I think you missed some .'s:

With Sheets("Class Roster Template")
    For Each rng In .UsedRange
        rng = WorksheetFunction.Substitute(rng, "/", "")
    Next rng
End With

With Sheets("Class Roster Template")
For Each rng1 In .Range("J2", .Range("J2").End(xlDown))
        rng1 = WorksheetFunction.Substitute(rng1, "M", "L")
    Next rng1
End With

You could also use Find/Replace instead of the Substitute function.

Dom

The dots in the suggested code(s) works.

Nevertheless I feel I must comment

Range(rangeA, rangeB)

will return a range from A to B

As this range is on the same sheet use

Range(.range("J2"), .range("J2").end(xldown))