Prior to install/upgrade, please check the system requirements from the Release notes.
There is no upgrade process actually as you can install any number of Spotlight of different versions in one machine. When the new version is installed then launched, the user will be asked to "Upgrade or create new Spotlight user". Just follow the wizard.
The Getting Started guide has the steps to install:
To install Spotlight from the downloaded installer from the Support Portal:
1. Close all open applications on your PC.
2. Execute the downloaded installer.
3. Follow the instructions on the screen to complete the installation.
Note: To cancel installation at any time, press Esc or click Cancel. If Spotlight is delivered as part of the Toad DBA Suite and you require multiple Spotlight
installations on your computer then contact Quest Software for more information.