The Server controls card on your service page has Reboot, Power off, and Power on. These are routine actions and take effect within a few seconds.
Reinstalling is different. It wipes the disk and rebuilds the server from a fresh image, so it's behind an extra confirmation step.
Reinstalling permanently erases all data on the server. There is no backup to restore from unless you arranged one. Take a copy of anything you need first.
After a reinstall, log back in with the same SSH key and root password from provisioning. On Managed WordPress, reinstalls are handled by our engineers through a support ticket rather than self-serve, so the site is handed back secured and ready to log in.