Upgrading Sencha ExtJs from 4.2.2 to 6.0.0

Question

My application's front-end was build long back on ExtJS version 4.2.2 ,so Sencha Cmd tool was not used at that time , I am new to ExtJS and wants to know what are the points should be taken care for migrating the ExtJS to from 4.2.2 to 6.0.0 ,My current plan is to install Sencha cmd tool and regenerate the js files ,Also to let you know that our backend is build on spring mvc ,version-5.2.21.RELEASE,

Some more technical details of my application are as below-
build tool used-gradle 6.9.1
As per the old standard of ExtJs, i have controller,View and Store Js files (MVC architecture)

Thanks in Advance