Are you using the plugin area to update the plugin or are you trying to upload the zip within the “Upload” screen of “Add Plugin”? When updating the plugin you have a few options. Typically most users simply use the Plugins area of the admin. I don’t believe the admin will support updating a plugin by using the “Add Plugin” Area’s Upload Zip functionality.
If you are trying to manually replace the files, you may be able to sftp/ftp into the server (depending on your hosting) and replace the plugin folder with the one from the zip that you manually downloaded from .org
If you are using the update plugin functionality in the PLugins list, it could be a permissions issue with your WordPress install
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This reply was modified 5 years, 10 months ago by Aaron Ware. Reason: Added more descriptive info