Deleting Oldest File

Greetings!

I am using this in a module to copy files to a directory:

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Public Function Backup()

Dim fso As FileSystemObject

Dim sSourcePath As String
Dim sSourceFile As String
Dim sBackupPath As String
Dim sBackupFile As String

sSourcePath = "c:a"
sSourceFile = "db2.mdb"
sBackupPath = "c:aa"
sBackupFile = "BackupDB_" & Format(Date, "mmddyyyy") & "_" & Format(Time, "hhmmss") & ".mdb"

Set fso = New FileSystemObject
fso.CopyFile sSourcePath & sSourceFile, sBackupPath & sBackupFile, True
Set fso = Nothing

End Function

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Now, what I want to do is delete the oldest file after there have been 5 files copied. In other words, I will be running this once a day and only want to retain the newest 5 copies. Once the sixth has been copied, delete the oldest one in the directory.

Any suggestions?