According to the listed DLLs and versions that are referenced in your project, it seems that you are using RadEditor Classic and RadControls for ASP.NET AJAX - the AJAX suite is combined in a single DLL. However, I am not quite sure how you have referenced two different versions of Telerik.Web.UI.dll.
Regarding upgrading RadControls for ASP.NET version you can find e detailed tutorial in the following KB article:
Updating RadControls for ASP.NET AJAX to another version or license
In general the latest version should be fully compatible with the 2009.2.826.35 one, except for few breaking changes which may or may not affect your application.
If you are planning to swap the classic editor that is used currently with its AJAX version you can follow the guidance from this help article:
Migration from RadEditor Classic to RadEditor for ASP.NET AJAX
the Telerik team
If you want to get updates on new releases, tips and tricks and sneak peeks at our product labs directly from the developers working on the RadControls for ASP.NET AJAX, subscribe to their blog feed