Assess your bee balm size in the fall. If it was just the right size this year, it's going to be too big next year, so you will want to trim it back. After the plant has died back in late fall, cut off all of the branches and drive a shovel down through the root to take off about 1/3 of it. Immediately plant this root section in another location. It will come back in the spring after its dormant period.
Trim and shape bee balm during growing season if necessary. Discovering that your bee balm is just plain too large in the middle of the flowering season isn't that much of a problem; simply pull away the stalks from the root and separate as much of the plant as needed. You can also use small gardening scissors or nips to cut them off and, if desired, you can shape the plant to better fit the landscape you've created.
Divide bee balm in the spring by driving your shovel down through the root ball, cutting off 1/3 to ½ of the root and planting it elsewhere.