If one image:

Right click on thumbnail, choose Set Categories

• Option A: To clear all tags, select Uncategorize all Selected Items

• Option B: To clear 1 tag, just go to the wrong tag and select it and it will unselect it.

If one or more images:

1. Click on the thumbnail or multiple thumbnails,

2. bring up your properties pane (View | Properties)

3. Find the tag and unselect the box next to the tag you don't want.