By default, Outlook displays toolbar buttons at the standard size. However, if you prefer to have larger toolbar buttons, you can modify the default settings that Outlook uses. Here's how you can make the necessary changes:
Select the Customize menu option on the Tools menu to display the Customize dialog box.
Ensure that the Options tab is selected by clicking it.
In the section labeled Other, check the Large Icons check box to enable large icons.
If later you decide you would like to revert back to using the smaller toolbar buttons, you can do so by simply removing the check from the Large Icons check box.