Simple Instructions:
To update the value of a piece of metadata, first choose the file to which that
value applies, and then the metadata element whose value you want to change.
Your selection appears in the metadata edit controls. Edit the value field and
click "Replace" to alter the metadata.
The process is the same when updating a folder with child folders or multiple files, but you can only update metadata that is common to all files/folders selected.
The value tree shows all previous values, not just those currently assigned.
Thus the value you have replaced will remain in the value tree.