1. Finder > Preferences > Sidebar > Tags > Recent Tags
2. All Tags
3. Select your tag
4. The number of items will be at the bottom
5. Delete by Right Clicking on the tag and selecting Delete Tag "[Tag Name]"

More Info: https://support.apple.com/kb/ph25325?locale=en_US

To view all the available tags in Finder, follow these steps:

1. Enable display of tags by going to Finder → Preferences → Sidebar → Tags → Recent Tags.

2. In the Finder menu, enable show Sidebar and Status Bar if they are hidden.

3. Under Tags section in the Finder Sidebar, click on All Tags.... This will display a list of all the available tags (pre-created + custom) sorted alphabetically.

4. Click to select a tag from the list. The count of files/folders associated with the tag is shown in the Status Bar.

5. To delete a tag, right click on it and select Delete Tag "Tag_Name"... from the context menu.

For more information on tags in Finder, refer to the Apple support document, macOS Sierra: Use tags to organize files.