In order to have Telerik® UI for ASP.NET AJAX running, you will need to have ASP.NET Web Forms installed on your development/production machine. ASP.NET Web Forms is available in the .NET 4.x+ installations. For example you can download .NET 4.8 from here.
Telerik provides the following installation package types that you can download from here:
MSI file for automatic installation. The Windows Installer Package (MSI) files are intended for easy and automatic installation of a product. The MSI installer unpacks the controls on your computer in a folder named Telerik in your Program Files. Additionally, the installer package adds the Telerik® UI for ASP.NET AJAX help files to your VS.NET IDE and to your local copy of MSDN (if you have one installed). If selected in the Feature Selection screen, the installer automatically adds Telerik® UI for ASP.NET AJAX Visual Studio Extensions and populates your Visual Studio Toolbox with the Telerik controls.
ZIP file for manual (advanced) installation. The ZIP is used for manual (advanced) installs and for upgrading/updating purposes. The folder structure is different from the Windows Installer (MSI) package. You need to be familiar with ASP.NET, IIS, setting permissions and creating virtual folders. It is a common practice to unpack the manual installation ZIP file directly to inetpub/wwwroot. Use the ZIP file for deploying on shared hosting.
NuGet package Telerik provides a NuGet feed that you can use to download only the necessary assemblies to get the project running. Additionally, you can also download the .nupkg files from Your Account in order to create a private company feed.
Source code (for licensed users only) is distributed as an archive named Telerik_UI_for_ASP.NET_AJAX_20xx_x_xxx_Source.zip and may be handy for educational or customization purposes of the controls. It may be also useful in scenarios when you'd like to check the private API of the controls as well as if there is some undocumented functionality.
The latest MSI and ZIP packages available for download already have all updates/HOTFIXES applied. There is no need to update them further.
If you already have Telerik controls installed by the MSI package, you can safely install an updated version—the installer will keep your existing installation. The new files will be placed in a separate folder and the new installation does not damage the common installer files. You can find more information and examples in the Major and Minor Releases Installation help article.