When configuring your server for the first time, you'll be prompted to choose your OS from the dropdown list and to enter your public SSH key ( optional )

After your server is set up, you'll receive an email with username/password combo to access it.
Also in the letter you'll receive you credentials to access Control Panel at https://panel.instinct.cloud
Further you'll be able to reinstall the OS both from panel and from your personal cabinet.
Reinstallation
As example, we'll take a look at reinstallation from personal cabinet.
When you open your server's page, scroll down to the OS list.

After you choose your desired OS, random password will be generated. You may type in your own password. Also you may enter your SSH public key.

When configuration is done, press "Start Reinstallation" button and wait for the process to finish. You have the ability to monitor the current state of reinstallation.
Feel free to contact our support if you've encountered any difficulties or have any questions.