We are trying to set up Roku and we don't seem to have the changers that allow to change the input to HDMI.

What changers are you talking about, there should be an imput for HDMI

I would call the store. They have support on.site

If older style tv there's a roku that will work for your t.v. if thats not the case check your input settings there be a way to look through the options, like volume or channel buttons.

Is it an older model TV that does not have HDMI inputs?? I would also suggest contacting the Xfinity store and explain the issue. They have helped me both times I have gone in with a problem.