First, be sure you're not streaming when not watching. Get in the habit of returning to the Roku's Home screen when done watching.
In case you forget the above Settings > Network > Bandwidth saver > On will ask if you're still watching when showing a channel with no user input received for 4 hours. If you don't respond it shuts down the channel and returns to the Home screen.
I've read there was a "secret menu" item reached by a specific sequence of key presses that could limit the requested resolution, but many channels ignored it, and that it was dropped from later software updates. Check the options on your individual channels -- especially the ones where you can log into your account on their websites.
Roku Streaming Stick +, 3810X, Ser YH0059427035, wifi - Samsung UN55ES6100
Roku Streaming Stick, 3600X, Ser 5S56D8240827, wifi - JVC EM37T