Need more specifics. What model Roku (number, not name), and you can find the model number of the remote beneath the batteries.
What do you mean by changing channels? Is this a Roku TV? Exactly which buttons work and which don't?
Have you replaced the batteries as a test?
Dan Roku Stick (3600), Ultra (4640), Ultra (4670), Ultra (4800), 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.