If you use 3rd party modules, check the developers site for compatibility and necessary updates.  Backup your DotNetNuke database and installation folder in file system, where DotNetNuke resides  create a copy of your web.config file download the appropriate package from www.DotNetNuke.com Source= core framework with souce code and all current core module versions (install versions, if available) Installation = same as Source, but without source code  Upgrade = core framework without source or module packages Check the forums at www.DotNetNuke.com for issues reported Stop your web site  in IIS If upgrading from DotNetNuke 3 to DotNetNuke 4: delete all .vb files in the DNN installation directory and subfolders delete all DotNetNuke dll files in folder /bin (Attention: not files of any modules!) use install instead of upgrade package  Unzip the package into the installation directory, make sure, that existing files with same name get replaces (pay attention: source version of DNN 4 has an addition root level with library and website folders, website constains the runtime files.  Note: the following section is optional for DNN versions as of 4.6.2. Starting with 4.6.2 a new function was added to the DotNetNuke core known as XML Merge, which removes the need for you to manually update the web.config file on each and every upgrade. For a detailed description go here, otherewise follow: rename release.config into web.config from previously used web.config copy the following entried into the new web.config both datenbase connection strings  both encryption keys  code Subdirectories in section SQLDataprovider copy keys DataBaseOwner ObjectQualifier check folder /install/modules for module packages, you do not want to install/upgrade. Since DotNetNuke 4.4.0, modules with appendix .resources don't get installed, but are made available for quick installation via menu item Host :: Module Definitions. If upgrading from DotNetNuke 3 to DotNetNuke 4 alter IIS settings for your Web Site or virtual directory switch ASP.Net version from 1.1 to 2.0  make sure, that applications using ASP.Net 1.1 do not share an app pool with ASP.Net 2.0 applications. If necessary, create a new pool.  start your web site in IIS  call your web site in your browser, this will start upgrade process and module installation  install additional or updated modules either using menu item Module Definitions or copy the packages to /install/module and call "/install/install.aspx?mode=installResources" install updates language pack(s) either interactively using Host :: Languages menu item or copy the packages to /install/language and call /install/install.aspx?mode=installResources