@QuincyV 

Have you enabled roaming under SITE > ADVANCED OPTIONS?  If this isnt enabled the devices are unlikely to roam at any real pace.

Also in the controller version 5.9.9 which is due out any day now, you can lock clients to specific APs

  @Philbert 

I have turned it on now. is it so good? i will update the controller.

  @QuincyV 

  @QuincyV 

Hey

That is the one, without that enabled the controller wont roam devices from AP1 to AP2, instead it will leave that decision to the device itself and they are awful at this.   Devices tend to stick to one AP unless instructed to roam.

You may also want to enable AI Roaming, Dual Band 11k. and Band Steering. 

AI Roaming.. - Basically smarter roaming, allow the controller to actively move devices as it feels necessary and not just when required.   This works well, recommend enabling it.

Dual band 11k.   Allows you to move from 2.4 on AP1 to  5ghz on AP2, this is generally a good idea and speeds things up

Band Steering.    The controller will move as many devices as possible to the 5ghz frequency, always the best option.   Set this to prefere 5/6ghz

Force dis-assocation..  its up to you really.  This is forced roaming.  In short if the device is old and doesnt support roaming, force it to move AP by kicking it off AP1 and onto AP2.   Its not graceful, but it works.    Personally i have it enabled on all my sites, rarely does it ever take effect.

  @QuincyV 

If you are a software controller, the update is already released under version 5.9.9

If you are a hardware controller (OC200 or OC300) then it will be a while longer for the firmware release, likely due this month.

  @Philbert 

Your inputs about the Site settings are very helpful.

Thank you for sharing

  @QuincyV Changing clients from one access point to another depends on the type of network you are using. If your network is based on a Wi-Fi router, you can adjust the settings in the router's administration page. You can switch the client manually or set up your router to automatically balance the load between all available access points.

  @PhilipMatrix 

This is only applicable to OneMesh or other Mesh enabled routers, this setup is not as common.  

Technically the 'router' doesnt actually do anything with the APs, thats the job of a controller to build and handle the SSID and clients.  However the controller may be built into the 'router' as a feature set (Deco for example).

Enabling automatic balancing is covered under Roaming and AI Roaming, which the origional poster has already enabled on the controller.