The terminology is a little misleading because you really don't *change* the
file format, you actually create a *copy* in the format you prefer. Just
open the file, tehn go to File> Save As, specify the name & destination
folder as usual for any new file but then open the Save As Type: list at the
bottom of the dialog. Select Rich Text Format (*.rtf) from the list, then
click Save or press Enter.