How do I install & activate ArcGIS Desktop?

Please jump to the section on Activating ArcGIS if you already have ArcGIS installed.
This guide is brought to you by Windows 7 and ArcGIS Desktop 10.5.

Install ArcGIS

1. Download the appropriate software.
2. Run the installer. You may need to wait a little but for a window to appear.
   
3. Accept any UAC prompts for an administrator account. If necessary, input your admin credentials.
   
4. Choose a destination folder.
   Optional: change the location.
   Press Next.
   
5. Wait for the files to unpack.
   
6. Make sure the box is checked to launch the setup program.
   Press Close.
   
7. Accept any UAC prompts for an administrator account. If necessary, input your admin credentials.
   
8. Wait for the installer to start.
   
9. System requirement: Microsoft .NET Framework 4.5 or higher. If you get the message about needing it, please go to https://www.microsoft.com/net/download/framework to download the latest version.
   
1. Visit the website
2. Select the latest .NET Framework only
   
3. Click the Download button
   
4. If asked, save the file
   
5. Run the file
   
6. Accept any UAC prompts for an administrator account. If necessary, input your admin credentials.
   
7. Wait for files to extract
   
8. Wait for the installer to finish
   
9. Press Finish.
   
10. If you get any sort of message and cannot continue, restart your computer.
    
11. Wait for Windows Update to finish
10. Find the location of your extracted files. Unless you changed it, go to your My Documents folder.
11. Open the ArcGIS folder.
12. Go into the Desktop folder.
13. Run the Setup file.
    
14. Accept any UAC prompts for an administrator account. If necessary, input your admin credentials.
    
15. Press Next on the Welcome screen.
    
16. Accept the License Agreement.
    Press Next.
    
17. Select where you want to install all ArcGIS features or some.
    We've chosen Complete.
    Press Next.
    
18. Optional, but not recommended: Change the ArcGIS installation destination folder.
    Press Next.
    
19. Optional, but not recommended: Change the Python installation destination folder.
    Press Next.
    
20. Optional: Join the Esri User Experience Improvement progam.
    Press Next.
    
21. Wait for ArcGIS Desktop 10.5 to install.
    
22. Press Finish.
    
23. Input License Information if it pops up, or skip to #_ in the next section

Activate ArcGIS with a license file

1. Open the Start Menu.
2. If needed, display All Programs.
3. Go to the ArcGIS folder.
4. Open ArcGIS Administrator.
   
5. Accept any UAC prompts for an administrator account. If necessary, input your admin credentials.
   
6. Select your product.
   ArcGIS Desktop
   Advanced (ArcInfo) Single Use
   
7. Press the Authorize Now button.
8. Choose the third option, I have received an authorization file.
   Press the Browse button.
   
9. Go to the folder where you have saved the provisioning file.
   Select it.
   Press Open.
   
10. Press Next.
11. If you are connected to the internet, choose the option to authorize using the internet.
    Press Next.
    
12. Leave all filled-in items for Information.
    Press Next.
    
13. Select options that are appropriate for you.
    Press Next.
    
14. Leave the authorization number as is.
    Press Next.
    
15. Leave the authorized extensions as their default values.
    Press Next.
    
16. Optional: Add an evaluation license for the Full Motion Video extension.
    Press Next.
    
17. Wait for the authorization to finish.
    
18. Press Finish.