In Manage → Content, select the files you want to update and choose Settings from their action menu.
Use Information for tags, Author and Description. Use Properties for fields active in the library.
Choose Save changes to apply your changes to the selected files.
What each change does
Add tags adds the entered tags while keeping existing ones. Remove tags removes the entered tags wherever they occur in the selection. If a tag is in both lists, removal wins.
Author and Description: entering a value replaces that field on every selected file. Leave a field untouched to keep each file’s current value.
Properties: changing a field replaces that property’s value on every selected file, including a field that allows several values. Other properties stay as they are.
Clear beside a property clears it on all selected files when saved. Undo cancels a pending Clear. Mixed values means the files currently have different values.
