The Tags option in the Organize menu lets you see your tags alphabetically, and view or edit every item associated with each tag across all lists:

Click the “edit” option (1) to open the tag editor, where you can either rename the tag (1) or delete it (2):

If you rename a tag to match another existing tag, they’ll automatically be merged.

When you delete a tag, it won’t erase the word itself from associated items — just the # symbol. This ensures you retain the original meaning in cases where the tag is embedded in the text — for example, #call Mike remains readable.