Follow the below to merge two departments into one:
Go to System Administrator Console, Attributes.
From Attributes set up, , click on Maintenance.
Locate Client Attributes.
Expand Department.
Locate the value you do not require, highlight it, right click, Supersede.
Locate Matter Details.
Expand out Department.
Locate the value you do not require, highlight it, right click, Supersede.
Locate Fee Earner Details.
Expand out Department.
Locate the value you do not require, highlight it, right click, Supersede.
You can then either delete the value if it’s no longer needed, or add a termination date so it no longer appears in lists.