How to Uninstall Yosemite? System does not allow Erase the HD, nor does it allow re-install of original O/S Disc (10.6.7). I want Mavericks or even Lion Back. Thanks.

Question

How to Uninstall Yosemite?  System does not allow Erase the HD, nor does it allow re-install of original O/S Disc (10.6.7).  I want Mavericks or even Lion Back.   Thanks.

Answer 1

Start with reinstalling Snow Leopard:
Clean Install of Snow Leopard
Be sure to make a backup first because the following procedure will erase
the drive and everything on it.
     1. Boot the computer using the Snow Leopard Installer Disc or the Disc 1 that came
         with your computer.  Insert the disc into the optical drive and restart the computer.
         After the chime press and hold down the  "C" key.  Release the key when you see
         a small spinning gear appear below the dark gray Apple logo.
     2. After the installer loads select your language and click on the Continue
         button. When the menu bar appears select Disk Utility from the Utilities menu.
         After DU loads select the hard drive entry from the left side list (mfgr.'s ID and drive
         size.)  Click on the Partition tab in the DU main window.  Set the number of
         partitions to one (1) from the Partitions drop down menu, click on Options button
         and select GUID, click on OK, then set the format type to MacOS Extended
         (Journaled, if supported), then click on the Apply button.
     3. When the formatting has completed quit DU and return to the installer.  Proceed
         with the OS X installation and follow the directions included with the installer.
     4. When the installation has completed your computer will Restart into the Setup
         Assistant. After you finish Setup Assistant will complete the installation after which
         you will be running a fresh install of OS X.  You can now begin the update process
         by opening Software Update and installing all recommended updates to bring your
         installation current.
Download and install Mac OS X 10.6.8 Update Combo v1.1 Access the App Store to download Mountain Lion or Yosemite. Mavericks is no longer available since the release of Yosemite. If you purchased Mountain Lion from the App Store, then you can redownload it via your Purchases page in App Store. If not, then you will need to purchase it from Apple;
Purchase a redemption code at the Online Apple Store: OS X Mountain Lion. Mountain Lion is $19.99 plus tax. Use the code to redeem a download of Mountain Lion from the App Store. The file is quite large, over 4 GBs, so allow some time to download. It would be preferable to use Ethernet because it is nearly four times faster than wireless.