On the Actions menu, the Synchronize submenu has commands that synchronize the current selection.
Update Left 
Copies newer and orphan files from right to left.
Update Right 
Copies newer and orphan files from left to right.
Mirror to Left 
Replaces all different items on left, deletes any orphans on left, and copies any right side orphans to the left.
Mirror to Right 
Replaces all different items on right, deletes any orphans on right, and copies any left side orphans to the right.