Hi box,
Thanks for posting your question. I'm more than happy to assist you today. All you need to do is change your nameservers to InMotion's nameservers. As long as the domain is the primary domain on your InMotion Hosting account, it's that easy. Please keep in mind once you make the DNS change, it can take up to 24 hours to take effect. Here's a link to our article on updating your nameservers:
Updating your nameservers
I hope this helps! If you need further assistance please feel free to contact us.
Thanks!
Tim S