Hi,
You have to use another cell (column, row, range or whatever) where you put converted cells.
formula for conversion is:
=UPPER(RANGE OF CELLS).
For example, to convert value in cell A5, click in blank cell (let's say B5) and type in: =UPPER(A1).
You can automatically fill in adjacent cells by dragging mouse down or right (or wherever).
Upon this, you can copy/paste converted values back to the desired location, instead of lowercase text.
Regards,
Almir