The Files area.
There is add button to add 100 files to be uploaded at once.
The upload control for Media and Videos.
This requires a modfications of the base FileUploadField that is calling the upload handler because the current upload is using RadUploadHandler. Create new upload handler (if the control is using such) for the related modifications of client component scripts. I can give you the implementation of the current upload field in support ticket since its a lot of code.
If just the styles of how the upload looks like need to be modified all styles are applied from Sitefinity backend theme which is available from Sitefinity SDK. Modify the them and use it instead of the default theme following this documentation.
To change the field which is a customized version of RadEditor specific for Sitefinity needs a new field control should be added that will implement the new functionality. To change the editor there are two options.
Go to Administration->Settings->Advanced->ContentView->Controls->(select a module for example news)->NewsBackend->Views->NewsBackendEdit->Sections->MainSection->Content and find the textbox field type where the editor is registered "Telerik.Sitefinity.Web.UI.Fields.HtmlField".Replacing it will require implementing a new control. I can send you the implementation of the HtmlField in a support ticket.
Another way is to create a field control with the silverlight control required. Here is post which is part of series of blog posts about field controls in Sitefinity.
Note all this this can prove to be tramendous effort.