If your VPS provider uses SolusVM as its VPS control panel, it's really easy to install Debian 6 on your VPS. Most unmanaged VPS providers that I've seen use SolusVM, so these instructions will work for a lot of VPS providers.
By the way, these instructions to install Debian 6 on a VPS with SolusVM are the same as for installing any operating system that's been made available by your VPS provider.
Log in to the SolusVM control panel
First off, log in to the SolusVM control panel of your VPS host, using the login information given to you by your VPS hosting provider. The log in information you will need usually comes in a welcome email sent to you by your VPS provider when you sign up for a VPS.
Note that these log in credentials are probably different from the root login and password for your VPS.
Click the "Reinstall" button
Once you're logged in to the SolusVM VPS control panel, you should see a section titled "Controls" at the bottom of the page. Under the "General" tab of that section, there is a button labeled "Reinstall" that you must click to start the reinstall of the operating system of your VPS.
Select Debian 6 from the list of available operating systems
Now you should see a page with a list of operating systems available for you to install on your VPS.
Since this article is about installing Debian, scroll down through the list of operating systems until you find Debian 6 listed. Choose between Debian 6 32-bit or Debian 6 64-bit and click the radio button next to your choice.
64-bit operating systems are generally recommended only for systems with more than 4 gigabytes of RAM. But some tests have shown that 64-bit operating systems perform better than 32-bit systems on systems with lower RAM.
Now that you've selected an operating system, scroll down to the bottom of the page and click the "Reinstall" button. Next, you will be asked to confirm your choice to reinstall your operating system. Click "Yes".
The time it takes for the reinstall process to complete can vary. I've had it take up to 10 minutes, and I've noticed it taking less than a minute.
To find out if your operating system has finished being reinstalled, scroll down the page and click on the "Back" button which will take you to the main administration page for your VPS.
On this overview page, you will see a button labeled "Log". Clicking it will take you to a page that will show you the status of your operating system reinstall request. The status of the operating system reinstall will initially say "Active". You can refresh the page with your browser.
When the status of your operating system reinstall is listed as "Complete", that means the installation of Debian 6 has finished and you can begin using your VPS.