I have just been writing this and it works. Be sure you place this in another database and have a copy of the database that you want to convert so you have a back up.
You have to add the file path and database name and then also do the same for the location and file name for the accde database.
Function ConvertToaccDE()
sourcedb = "C:\Users\Trevor G\Documents\sample back.accdb"
targetdb = "C:\Users\Trevor G\Documents\sample back.accde"
Dim accessApplication As Access.Application
Set accessApplication = New Access.Application
With accessApplication
.SysCmd 603, sourcedb, targetdb
End With
'Set accessApplication = Nothing
End Function