Both actions live in the VPS control panel in your client area.
- To reboot cleanly, log in over SSH and run
sudo reboot. If the server is unresponsive, use the Reboot button in the control panel to force a power cycle. - To reinstall, open the control panel, choose Reinstall (or Rebuild), pick your operating system template, and confirm.
Warning: a reinstall wipes the entire disk and gives you a fresh OS, so back up any data and configs first. After reinstalling, you'll get a new root password (often emailed or shown on screen) and will need to reconfigure your software. On unmanaged plans this is your responsibility; managed customers can open a ticket for help.