Version 2.5 is backward compatible by API with versions 2.0 and 2.1 ( separate components is mostly compatible with version 1.6 as well ), so you will not need to made any special updates in code, while updating codebase to the version 2.5
If you are using layout, accordion or tabbar then you will need to add the “dhtmlxcontainer.js” on the page. All above components doesn't require “dhtmlxWindows” anymore, and are fuly functional separately.
Beware that dhtmlx.js, included in package, is compiled with dhx_skyblue skin, so if you are using the different skin - you will need to change skin in your code or recompile the dhtmlx.js through libCompiler. ( by the way, in case of components 2.5 you can change default skin for all component on the page , by simple defining dhtmlx.skin=“skin name” )
If after update, you start to receive “dhtmlx is undefined” error - be sure that