Go to https://my.datarealm.com/ and log in. The username is your email address, and the password is the one you entered on the signup form.
Once you are logged in, go to "View Servers" under "My Services" on the left.
Click on the icon in the "Action" column for the server you wish to reboot.
On the right, click on "Remote Reboot" and confirm the reboot when the alert box comes up.
Depending on the operating system and the date of the last reboot, the server should be back up in anywhere from 1 to 10 minutes.