@robertburr,
Indeed, WordPress will not allow you to install the same plugin twice.
You would have to first delete MailPoet 3.6.1, then upload and activate the new version of MailPoet 3.6.2.
Otherwise, as you’ve seen, WordPress will not allow you to install the new plugin version and will instead return an error “Destination folder already exists”.
Existing MailPoet data is retained on plugin deletion, so you should not lose any information.
Best regards,
MailPoet Team.