HD default setting

A Comcast  technician set our system so the TV automatically defaults or reroutes to HD channels when we choose a non-HD channel. We can see all the channels on the Menu but when we select a non-HD channel it goes to the HD version of that channel.  How can we revert back to selecting the channel we want, either HD or non-HD?  I don't know whether this is a setting within the Samsung TV setup and remote or within the Xfinity system and XR11 remote.