Select the unlocked dimension or locked dimension you want to change.
On the command bar, click the Lock button. This is a toggle button that specifies the dimension behavior.
--When this option is cleared, it is unlocked (driven).
--When this option is set, it is locked (driving).
When you change the dimension behavior, the color of the dimension also changes.
Tip:
If the Lock button is not available, select the Maintain Relationships command on the Home tab or the Sketching tab.