Recombining 5 ghz and 2.4 ghz on Airport Extreme

I have found that this is not the best performance for my various devices and followed some instructions to 1. open airport utility 2. choose Airport Extreme 3.chose edit 4. choose wireless network 5. choose wireless options 6. deselect the checkbox for 5 ghz network name.

You did everything correctly.

For reasons that Apple does not explain, the presence of your previous 5 GHz network will remain as a selectable option in your Mac's Wi-Fi menu for a time. If you de-selected the separate 5 GHz network name in AirPort Utility as you wrote, attempting to connect to it using your Mac's Wi-Fi menu will fail.

Its name will eventually disappear from the Wi-Fi menu. I don't know how long that takes.

High‑performance 802.11n in a double dose.

AirPort Express supports simultaneous dual‑band 802.11n Wi‑Fi. That means it transmits at both the 2.4GHz and 5GHz frequencies at the same time. So no matter which band your wireless devices use, they’ll automatically connect to the best available band for the fastest possible performance.

If you enable the 5ghz, the name will be amended to show the 5ghz so you will know the difference between the 2. You can only join one network at a time. They are not the same or unified and should show separately. As to which your device chooses, that has to be set in the device's default as to which is the preferred.

So you have disabled the 5ghz band. Where are you seeing that name option for that network? If in system preferences, you are referring to the network advanced wireless settings and the list of networks, you would just remove it from there. It will stay in memory until you do.

I understand now. You did not enable the separate name before. And you already forgot the network in preferences.

As John said, it will disappear.