If your Windows 10 Spotlight wallpaper is not changing then do the following steps:

  1. Open Settings panel by pressing Win+I and go to Personalization > Lock Screen. Under the Background option, choose Picture and set a picture as default lock screen background.
  2. Navigate to the following folder:
    C:\Users\<username>\AppData\Local\Packages\Microsoft.Windows.ContentDeliveryManager_<characters>\Settings
  3. Delete the two files called roaming.lock and settings.dat
  4. Start Windows Powershell as administrator
  5. Copy and paste the following command:
    Get-AppxPackage Microsoft.Windows.ContentDeliveryManager -allusers | foreach {Add-AppxPackage -register "$($_.InstallLocation)\appxmanifest.xml" -DisableDevelopmentMode}
  6. Open Settings panel by pressing Win+I and go to Personalization > Lock Screen. Under the Background option, choose Windows Spotlight
  7. Done!  Check out your new lock screen background by pressing Win+L