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Restart the TV
If there is nothing wrong with the remote control, i.e. no button is stuck both on the remote and the TV, turn it off and back on after a couple of minutes.
In addition, you can do a "power reset" of the TV, if you unplug the TV from the power socket and press and hold the power button (on the TV, not on the remote control) for at least 10 seconds. Then, plug it back in the electrical outlet and turn it on.
Maybe a channel-switching button (e.g. the channel + or - buttons or a channel-number button) on the remote control or on the TV itself is stuck. All you need to do is to unstick the stuck button and the TV will stop changing channels by itself.
Cover the remote control's front edge (the IR sensor) to check if the TV will stop changing channels. If it does, then a button on the remote control may be stuck. If it doesn't then a physical button on the TV might be stuck.
Check if another remote control is compatible with your TV
If you have more than one remote control, it is possible that the other remote control is partly or fully compatible with your TV. In this case, when you use the remote control with the other device (e.g. another TV, DVD/Blu-ray player, etc.) your TV picks up the signal. All you need to do is to place the other device away from your TV so that your TV doesn't pick up the signal.
Disassemble the remote control and clean the buttons and the board
Over time the buttons (the keypad) and the circuit boards of remote controls get greasy, which results in some buttons getting stuck. If the buttons stuck when you press them, you need to disassemble the remote control and clean the buttons.
Feel free to watch the video below to see how greasy buttons look like and to learn how to clean the remote control:
If your TV's IR sensor (the sensor which picks up the signals sent from the remote control) is exposed to direct sunlight, your TV might be led into believing that you are changing channels. Also, if a neighbor owns a similar TV as your own, your TV might be picking up the signal sent from your neighbors remote control.
All you need to do is to reposition the TV, i.e. move it away from window and direct sun exposure.
In some rare instances, usage of another wireless infrared devices in close proximity to the TV may cause this type of issue. To be on the safe side, move all wireless and infrared devices away from the TV.