BlueHost (my.bluehost.com)

1. Log in to your account at http://my.bluehost.com.
2. Select the DNS Zone Editor in the Domains section.
3. Select the domain you wish to modify from the drop down menu.
4. Scroll down to the section Add a DNS Record.
5. For the Host Record, enter only the subdomain of the address you want to use for your Instapage custom Domain. For example, if you picked lander.mydomain.com as your address, enter lander here. Or, if you're using a root domain such as www.mydomain.com then you'll want to enter www here. Do not leave this blank.
6. Select CNAME from the Type dropdown menu.
7. Enter pageserve.co as the Points To value.
8. Click Add Record Now. You may need to wait up to a couple of hours for the CNAME to function.

For more information, you can access BlueHost's support documentation