Under Sales/contribution types/articles/edit, swap, summarise merchandise categories you can edit merchandise categories in the following window:

1. Via New you can create a new product group.
2. If you log in to the New you have made a mistake, you can use Edit (F7) to correct your entry.
3. You should only delete a product group if Delete, if the merchandise category is no longer used in the articles. If you delete a merchandise category that is still used in the articles, the short form of the merchandise category is saved in the article text.
4. Under Swap merchandise categories in the items the following window opens, which you can close after making the settings with OK after making the settings.