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.