Available from Optuma 2.0 and onward, the exchanges displayed in the Optuma Security Selector (F3) can be sorted by Default, Alpha or Last Used Order.
To adjust the order of the Exchanges open the Security Selector window by pressing F3 on your keyboard, or by going to New - Single Code Chart - Bar Chart.
In the window that opens, right click on the Exchange folder at the top of the list (far left side).
In the menu that appears, at the top will be an option called Sort Exchanges By. Click on the drop down arrow to select the desired exchange order you wish to use.
Note: Any newly added exchanges (imported via a 3rd party for example) will not be ordered until the next restart.