Convert ASC to TXT

Both ASCII (.asc) and TXT (.txt) files are just text files so editable using any text editor and you can rename the extension freely. Any decent text editor allows for changing of encoding, which is what is what you might have been actually looking for.

It might also be very well possible that you have been looking for a way to convert ASCII numbers to a text in which case it would be best to use websites like ASCII to text converter.