Press and hold the Menu button (the center section with the + and - buttons to the sides) until you hear a beep (3 seconds or so). After that, when you press and release the Menu button, the Channel number should flash indicating that you can change the channel. In the future, you can toggle the keypad lock by pressing and holding the Menu button.
You can find more information on the Keypad Lock feature in the manual. See page 14 and page 21. The manual is available from ManualsLib: https://www.manualslib.com/manual/106993/Motorola-Talkabout-T5320.html . For the diagram of the Motorola Talkabout T5320, see https://www.manualslib.com/manual/106993/Motorola-Talkabout-T5320.html?page=14#manual . The Keypad Lock is described here: https://www.manualslib.com/manual/106993/Motorola-Talkabout-T5320.html?page=21#manual .
I hope this helps. I usually use my Motorola Talkabout radios with the keypad lock active. I hit the various button accidentally when working in the field.
Cindy Wells
