You may decide that you would like to change the text in a comment box. To do this, follow these steps:
Click on the appropriate cell.
Right-click and select Edit Comment from the drop-down menu (alternatively, select Edit Comment from the Insert menu).
The comment box is displayed with its text. The box will remain visible on screen till you click outside it.
Click in the box and edit the text as you would with any other text (with the proviso that you can’t apply any font effect).
Once you are satisfied, click outside the box to close it.
You can edit the comment at any time and as many times as you like.
See: