Greetings to all

I'm making a range of ISO shipping container, ranging from 10 to 40 feet in length and of different height. I have started with a 40 foot container by making an assembly with the container fitting corners (see screenshot 40 ft. Container (ISO-1AA) - Screenshot 01) There is apparently a possibility to lock mates between components such as in screenshot 40 ft. Container (ISO-1AA) - Screenshot 02. I have tried it but ones I have locked the components, I can't unlock afterwards. Could someone please tell/show me the correct procedure of locking/unlocking mates/distances between parts/components in an assembly.

Thank You kindly in advance

With kind regards

Orfeo Lauffer