1. Click the desired layer, and Click the Appearance tab on the ribbon.
2. Click Symbology.
3. Select 'Graduated Colors' or 'Graduated Symbols' in the 'Symbolize your layer by quantities' section.
4. Click the More drop-down arrow > Symbols > Reverse Order.
This reverses the order of symbols and leaves the upper value order unchanged. This allows all symbol classes to display.