Generally you can do the following:
1. login to account.lunarpages.com
2. click on "control panel"
3. then you should see a link that says "go to cpanel/plesk/lpcp" (last depending on your account type)
If you can not login or you get error after clicking on the "go to" link, you may need to contact support at support.lunarpages.com / firstname.lastname@example.org