The latest OS supported on a Late 2008 Aluminum MacBook is OS X 10.11.6 and can be downloaded from this link which will open in the App Store.
Note that while is starts off saying "This version of OS X El Capitan is for users running OS X Snow Leopard...", it also says...* "This version of El Capitan can also be used on Mac computers that are not compatible with Sierra.".
You can use the instructions in Create a bootable installer for macOS to create a USB Installer to do a clean install of OS X El Capitan.
Use the 'createinstallmedia' command in Terminal
- Download the macOS installer from the Mac App Store. Quit the installer if it opens automatically after downloading. The installer
will be in your Applications folder.
- Mount your USB flash drive or other volume. You could also use a secondary internal partition that has at least 12GB of available disk
space for the installation files.
- Open the Terminal app, which is in the Utilities folder of your Applications folder.
- Use the
createinstallmedia command in Terminal to create the bootable installer. For detailed usage instructions, make sure that
the appropriate macOS installer is in your Applications folder, then
enter one of the following paths in Terminal:
Path for El Capitan:
/Applications/Install\ OS\ X\ El\ Capitan.app/Contents/Resources/createinstallmedia
This is the basic syntax of the command. Replace
volumepath with the
path to your USB flash drive or other volume, and replace
installerpath with the path to the Install OS X app.
createinstallmedia --volume volumepath --applicationpath installerpath
The following examples assume that the OS X installer is in your
Applications folder and the name of your USB flash drive or other
volume is MyVolume:
Example for El Capitan:
sudo /Applications/Install\ OS\ X\ El\ Capitan.app/Contents/Resources/createinstallmedia --volume /Volumes/MyVolume --applicationpath /Applications/Install\ OS\ X\ El\ Capitan.app
After creating the USB Installer, you can boot the Mac with it and do a clean install. Make sure you backup anything you do not want to loose before erasing the HDD and installing OS X El Capitian.