I do hope you took a backup and have a safe copy of it before you started the first upgrade.
Your kernel is too old, because your OS version is very old. As pointed out upthread, you have limited options for updating your kernel.
Upgrading your OS in place will probably be lengthy and difficult. The usual advice is to start up a fresh new OS, install discourse, and restore your backup. (Ideally, don’t delete anything existing until your new world is completely working. If you end up on a new instance with a new IP address, you’ll need to update your DNS)
If you can ssh to your discourse server then you should be able to use ‘scp’ to copy a file to your PC. I don’t know if Putty directly supports that. But if you use Linux or any unix-like shell on a Windows machine, you should have scp.
The only “important” thing that isn’t included in the backup is your /containers/app.yml configuration file. It contains among other things your plugins list if you have any. It can be a good idea to copy this somewhere so you can install them on your new instance. The plugins’ settings, however, are stored in the database which is in the backup file.
Personally, I would want to be 100% confident that the backup is complete and correct, and so I would want to bring up a new install and successfully restore, before I destroy the old one. This does mean briefly paying for two instances from your hosting provider.
I should also declare that I have never yet needed to try a restore. So I am inexperienced in the practice.