How do I change the Wi-Fi name (SSID) and/or password?

Go to WLAN > WLAN 2.4G > Basic Settings. Update Primary SSID and WPA Passphrase, then click Save & Apply.
Repeat under WLAN > WLAN 5G > Basic Settings for the 5 GHz band.

Tips: If Band Steering or MLO is active, both bands share the same SSID. Change it once in WLAN > Advanced > MLO.