If you used the imqbrokerd command from the command line to connect the brokers into a cluster, you must stop each of the brokers and then restart them, specifying the new set of cluster members on the command line:
Stop each broker in the cluster, using the imqcmd command.
For example, suppose you originally created a cluster consisting of brokers A, B, and C by starting each of the three with the command
imqbrokerd -cluster A,B,C
To remove broker A from the cluster, restart brokers B and C with the command
imqbrokerd -cluster B,C