Using the ASC function:
The text in the source cell (C4 in this example) is not altered itself and the formula cell (C8 in this example) contains only the result of a formula and not the text itself. To store the cleaned up text in cells, you can select and copy the cells that are using the ASC function and then do a Paste Special to paste only the cleaned up text and into the destination cells.
The arguments for the ASC function are:
|text||Required||the text or a reference to a cell that contains the text you want to change. If text does not contain any full-width letters, the text is not changed.|