M-Language functions (use dynamic file location)

How do I tweak the function below in order to dynamically fetch a file's location?

(currently, source is hard coded) - thanks!

(CleanUpParticipants) =>

let
    Source = Csv.Document(File.Contents("C:\Users\Participants_January2018.txt"),[Delimiter="	", Columns=2, Encoding=1252, QuoteStyle=QuoteStyle.None]),
    #"Promoted Headers" = Table.PromoteHeaders(Source, [PromoteAllScalars=true]),
    #"Changed Type" = Table.TransformColumnTypes(#"Promoted Headers",{{"Participant", type text}, {"ID", Int64.Type}}),
    #"Split Column by Delimiter" = Table.SplitColumn(#"Changed Type", "Participant", Splitter.SplitTextByDelimiter(",", QuoteStyle.Csv), {"Participant.1", "Participant.2"}),
    #"Changed Type1" = Table.TransformColumnTypes(#"Split Column by Delimiter",{{"Participant.1", type text}, {"Participant.2", type text}}),
    #"Renamed Columns" = Table.RenameColumns(#"Changed Type1",{{"Participant.1", "First Name"}})
in
    #"Renamed Columns"