There is no problem to change the CNAME records for your domain.

SiteGround customers can request this service from:

Customers' Area --> Get Support --> Report hosting related issue --> Domain/DNS issues

You should post a general ticket there and provide us with the CNAME records you would like to be added to your domain's DNS.

If you are not a SiteGround customer, you should be able to edit your CNAME records from the control panel at your host/registrar. For more information on how to do this you will have to contact your host/registrar.

Alternatively, you can sign up for a hosting account with SiteGround and let us take care of your domain's DNS records for you.