I installed some MR45 on the network but the clients are connected to 802.11n (Channel 6 - 20 Mhz wide) or sometimes the AP changes the mode 802.11ax giving the highest speed to the user. How set to use only 802.11ax?
The question that is the bane of network admins everywhere who use WiFi. How do I make it fast?
This is a huge multi-part question as there isn't a checkbox to make everything use 802.11ax. What devices are we talking about and are they even 802.11ax capable? What kind of interference do you have around these APs? What type of Radio Profiles are you using with your APs?
These are just a few of things that can affect WiFi performance.
You mention channel 6 - which is 2.4Ghz. I would only using the 5Ghz band (under SSID settings). Make sure you increase the minimum bit rate to at least 12Mb/s as well.