Editing a tag is as follows: Swipe the desired tag to the right, as shown in the picture below.

Once the tag has been swiped 3 buttons are displayed:

• The button on the left allows you to specify a color to the tag.
• The button in the middle with the pencil icon allows you to edit the name of the tag.
• That trash button on the right deletes the tag.

When specifying a color a pop-up menu is displayed, as shown in the picture below, and the desired color can be selected.