Implementing Cisco IP Switched Networks (SWITCH v2-0) (#269)

What is the easiest way to force a specific switch to become the spanning-tree root bridge for a VLAN?

Raise the spanning-tree priority value on the switch.
Lower the spanning-tree priority value on the switch.
Raise the port-cost value of an interface on the switch.
Lower the port-cost value of an interface on the switch.