Help getting started with Roku devices, including setup, connecting your device to your TV, linking a Roku device to your account at my.roku.com/link, adding channels, subscribing to services, and more.
That sounds like the zoom feature of your TV has been enabled. The Roku itself has size settings. It has resolution settings, that doesn't force text off screen if you choose a resolution that doesn't match your display's native resolution. Look on the remote for your TV and look for a picture size or aspect ratio button. You also might have to look in the TV's display settings.
This is assuming you are not referring to a Roku TV, but a Roku player.
Dan Roku Stick (3600), Ultra (4640), Ultra (4670), Premiere (3920), Insignia 720p Roku TV, Sharp 4K Roku TV, Nvidia Shield, Windows 10 Pro x64 running Serviio and Plex on a wired Gigabit network.