You must perform the installation from an account that has administrator privileges. Installing via a non-administrator account is currently not supported.
If you have installed a previous version of the App Inventor 2 setup tools, you will need to uninstall them before installing the latest version.
Follow the instructions at How to Update the App Inventor Setup Software.
Download the installer.
Locate the file MIT_Appinventor_Tools_2.3.0 (~80 MB) in your Downloads file or your Desktop. The location of the download on your computer depends on how your browser is configured.
Open the file.
Click through the steps of the installer. Do not change the installation location but record the installation directory, because you might need it to check drivers later. The directory will differ depending on your version of Windows and whether or not you are logged in as an administrator.
You may be asked if you want to allow a program from an unknown publisher to make changes to this computer. Click yes.