I was looking around WHM, and it doesn't appear that you can change the docroot (document root) for Apache there. There are multiple articles that describe how you can change docroot for Apache in the Apache configuration file. You need to be an administrator with root access to the server. The default document root for InMotion Hosting accounts is "public_html".
You can see how to change it in this post. Make sure you make a backup BEFORE you make any changes to your web server configuration file. InMotion Hosting uses CentOS, so be sure you're looking at those steps in the article. If you're not familiar with making changes with the Apache server configuration file, then please contact technical support, or speak with an experienced tech before making the change.
If you have any further questions or comments, please let us know.