Ext JS 2.0.2 to 4.x Migration

I have a web application using extjs 2.x and now I would like to upgrade to extjs 4.x

Is it extjs 2.x not compatible with extjs 4.x and do I need to rewrite the web application?

Any release note / web page show the difference between Ext JS 2.x / 4.x ?

Ext JS 2.0.2 to 4.x Migration