1. Download and install the 7-Zip application onto your system.
2. Right-click on Rhino 5 installer file.
3. From the menu, select 7-Zip and Expand.
4. Select file location to expand contents to and remember it.
5. Browse to this folder and look for the Installers subfolder.
6. For 64-bit systems only: Double-click rhino5setup_en-us_x64.msi and complete the installation.
7. For all systems:
   1. Double-click rhino5setup_en-us_x86.msi and complete the installation.
   2. Double-click LanguagePack_en-us.msi (and any other languages you wish to install).
   3. Double-click HelpMedia.msi.
8. If you experience errors during installation:
   1. Write down any error numbers and messages you see.
   2. Email the step you are on in this article and any errors to tech@mcneel.com.
9. Restart Windows if prompted.
10. Start Rhino 5.
11. In the Rhino 5 command line, type ToolbarReset then press Enter.
12. Close Rhino 5.
13. Start Rhino 5.
14. Installation is complete!

The same process for V4 is described here.