Updating plugins manually

I feel a bit silly asking what is possibly a very basic question, but two of the plugins I’m using are purchased and updates are not reflected in the plugins panel. Notification of them was emailed with a link to a zip file.

Neither of them have any instructions as to how to update..and neither developer responds when I ask how to update.

Do I just unzip them and copy the files over the existing plugin files on the server? How would I know if there is a change to the DB?

Thank you