If you are upgrading from 4.1.19.2 then you can do the following step.
Backup, Backup, Backup, Backup
a) Backup the Database with PhpMyAdmin or Navicat / HeidiSQL etc Make sure you have a full backup to revert to (just in case)
b) Backup all files, use Cpanel / Filemanager to zip all the files, and download the zip file
Once you have a backup, all you need is to extract the release to the desktop or to the server
Uploaded the extracted files and overwrite all the old ones (You already have a backup)
Go to yourdomain.com/forum/upgrade (if its not in /forum it could be just be /upgrade)
Login and follow the instructions, do not switch windows and just leave it to upgrade.
Profit