It is not quite as simple as uploading all the files and pressing a button.
right now you have uploaded the folder named install. as long as that folder is there you can't see your board.
however, you probably uploaded the new blank config.php file to overwrite the one you had.
if so, you have to rebuild it so that you can upgrade. without a proper config.php file the board will not work.
so, using ftp, check to see if your config.php file is zero bytes in size. if so, do this:
Knowledge Base - Rebuilding Your config.php File
once you have the config.php working again you can proceed with the upgrade instaructions found here:
https://www.phpbb.com/support/docs/en/3 ... /upgrade3/
be sure to follow all instrutions exactly in order.
this means always always make backups of the database and the files before you start.