On the Tools menu, click Customize.
Make sure the toolbar you want to change is visible.
How?
In the Customize dialog box, click the Toolbars tab.
Select the check box for the toolbar you want to display.
In the Customize dialog box, click the Commands tab.
With the Customize dialog box open, do one of the following:
Assign or change a toolbar button's keyboard shortcut
Click the button on the toolbar (On the top toolbar, not in the box)
In the Customize dialog box, click Modify Selection.
In the Name box, type a name for the toolbar button with an ampersand (&)
before the letter that you want as the keyboard shortcut.
Press ENTER.
Assign or change a menu command's keyboard shortcut
Click the menu name on the menu bar (menu bar: The horizontal bar below the
title bar that contains the names of menus. A menu bar can be the built-in
menu bar or a custom menu bar.) or toolbar.
Click the menu command.
In the Customize dialog box, click Modify Selection.
In the Name box, type a name for the menu command with an ampersand (&)
before the letter that you want as the keyboard shortcut.
Press ENTER.
In the Customize dialog box, click Close.