I wonder if he is talking about channel width ...I do not know what the term "rf mode" means in relationship to wifi.
Can you be more clear what you want to change.
Most wifi parameters are negotiated between your PC and the router. The 2 devices try to pick the best data encoding they both support. The router has most the control. On the pc you can sometimes select between different options that the router supports like if you want to use 2.4g or 5g.