To remove tags from multiple files at the same time:
Click the Files page on the left-hand navigation.
Select all of the files to which you would like to remove Tags by clicking the checkbox next to the file name.
Scroll to the bottom and click the Tag icon.
Click Add and Remove Tags.
Click the Tags box and select the Tag you would like to remove from the selected files.
Click back into the Tags field to remove additional Tags.
Click Remove Tag.
Related article: How to Add Tags to Multiple Files at Once