You configure LACP system priority on each device running LACP.
LACP uses the system priority with the switch MAC address to form the system ID and also during negotiation with other switches. The system priority value must be a number in the range of 1 through 65535. The higher the number, the lower the priority. The default priority is 32768.
device# configure terminal
device(config)# lacp system-priority 25000
device(config)# no lacp system-priority