Here's how:
1. open a company card
2. change the address in the Address field in the Company tab
3. click on Save and Close
4. re-open the company card
5. click on the Contacts tab
6. select all of the contacts (click on the first contact, hold down the Shift key, click on the last contact) or multi-select a few contacts (click on one of the contacts, hold down the Ctrl key, click on the other contacts you want to change)
7. right click on one of the contacts and select Update Addresses
8. click Yes when asked if you want to continue