Go to space administration section, and click Bulk Labels Manager
By selecting equal, in listbox, all labels matching one of thoses in the textarea, will be replaced with the one in the second textbox, and by selecting containing, in listbox, all labels containing one of thoses in the textarea, will be replaced with the one in the second textbox
By selecting equal or containing, in listbox, all labels matching one of thoses in the textarea, will be deleted.
By searching different patterns of the same label, and replacing them by one label, you make your labels merging.