make sure your Gateway offers both, in your wifi settings if you dont have 2 seperate wifi networksshowing that means there sharing the same name. in that case you would seperate the network names EXAMPLE: for 2.4 MY_WIFI and for the 5GHz MY_WIFI-5. Keep same passwords for both to make it easy for your self. you can change your wifi names by going thru the comcast app, logging into you online account going to the internet tap or logging`into the gateway(may need to log in if the 5GHz was shut off not using the same name).
The primary differences between the 2.4 GHz and 5GHz wireless frequencies are range and bandwidth. 5GHz provides faster data rates at a shorter distance. 2.4GHz offers coverage for farther distances, but may perform at slower speeds