To quickly get rid of ‘another update in process’ message, you need to delete the core_updater.lock option from your WordPress database.
The easiest solution: Fix Another Update in Process Error Using a Plugin
First thing you need to do is install and activate the Fix Another Update In Progress plugin.
Upon activation, you need to visit Settings » Fix Another Update In Progress page. If updates on your website are locked, then you will see a message with WordPress Update is locked. You need to fix it and a button to fix it.
Simply click on Fix WordPress Update Lock button to continue.
The plugin will delete the WordPress core update lock option from your database, and you will see a success message Success! You’ve successfully fix to another update in progress!
You can then continue to the WordPress upgrade.