To quickly resize all the characters in your notebook including the characters in the output regions:
Select the part of a notebook you want to resize. If you want to resize fonts in a whole notebook, select Edit>Select All.
Select Format>Increase size or Decrease size.
Note: Graphics size does not change.
To change graphics size, see Scaling Graphics.
To undo font size changes, select Edit>Undo or use the toolbar button .
Note: Using the opposite option (such as increasing the fonts you have decreased before) does not guarantee to restore the original font size.