You can change the sort order of the labels in a map legend to display their values in ascending or descending order.
About ascending sort: For thematic legends, an ascending sort means the rows display in a top to bottom manner that makes sense for the particular theme type; for example, a Ranged theme frame that displays the rows from lowest to the highest range. For a Pie or Bar theme, an ascending sort means the categories are listed in the order selected by you. For an Individual Value legend, the label sort order is based on the original order of the items when the theme was created. This also means that changing a text label for Individual Value themes does not affect the sort order.
About descending sort: For thematic legends, a descending sort means the rows are displayed in a bottom to top manner that makes sense for the particular theme type. For an Individual Value legend, the label sort order is based on the order of the items when the theme was initially created; for example, an Individual Value legend theme would display rows alphabetized from Z to A. However, changing a text label for Individual Value themes does not affect the original sort order. For Graduated Symbol legend, a descending sort means the values are listed from largest to smallest.
To change the sort order of labels in a map legend in a Legend Designer window:
- Double-click on the legend, or right-click on it and select Modify Legend Frame Properties from the pop-up menu.
-
In the Legend Frame Properties dialog box, click Sort Labels in Ascending Order
or Sort Labels in Descending Order 
.
- Click OK.
The Legend Designer window refreshes with your changes.
To return to the default sort order, double-click on the legend and then click Clear Sort 
. This button only displays for map legends, not thematic legends. Map legends have a default sort order, which Clear Sort restores.