To change the article tags, you need to first create a new tag, then delete the existing tags. Tags weren't meant to change regularly, so there is no simple workaround. You need to make sure all panels are updated if you change tags.
Create a New Category
First, create a new category by navigating to Articles and then to an article you want to assign a new category. If you do not have an article that you want to put into the category yet, pick any article. You can unassign it from a category at a later date.
Assign it to the New Category
Next, you need to assign it to that specific category. Simply click on the category. Be sure and save your changes.
Navigate to the page containing the panel for the articles. Highlight the panel and click the panel browser button.
Assign Proper Category
Next, you'll assign the new category and remove the old category. Save the changes.
Remove Old Category and Delete
Remove old category.
Confirm the Articles publish properly