Design options are the features which needs to be selected during design period. For instance if you want to wish that a components should be connected with a crystal and not with a clock, then you can use a option. You can change the addresses, voltage options or booting option by exercising this feature. Some of the feature are auto detected selected for circuit design on which you not have a control. For instance RMII/MII selection power on configuration logic is selected by the AI engine.
To change configuration options follow the steps outlined in the link below:
Once the component is selected by circuit tree click on the icon shown below to open the configuration option menu which is custom for every component.
In the pop up menu select the drop down option from different tabs.
In case you are not sure or dont enter any values circuit tree will automatically preselect the options based on what it thinks is the best option.