OP:
I would suggest either El Capitan or Sierra as better OS's than Yosemite.
If you REALLY want to "go back", here's how to do it:
You will need:
- An external hard drive
- CarbonCopyCloner (CCC is FREE to download and use for 30 days)
- A copy of the OS installer of your choice.
- A USB flash drive 16gb or larger
- ONE of the following: "Boot Buddy", "DiskMaker X", or "Install Disk Creator" (all are free)
How to proceed:
First -- use CCC to create a cloned HFS+ backup (important that you use HFS+ and NOT use APFS) of your current internal drive to the external drive. Then, just set it aside for now.
Next -- use one of the 3 apps above to create a BOOTABLE flash drive installer using the OS installer you chose. Very easy to do, app will walk you through it as it runs.
Next -- boot from the USB flash drive installer (press power on button, hold down option key until startup manager appears, select flash drive with pointer and hit return).
BUT -- DON'T begin the install yet. Instead, open Disk Utility and ERASE the internal drive to HFS+ with journaling enabled.
NOW -- go back to the installer and install the OS. When done, it should present you with the setup screen.
Next -- connect the cloned backup to a USB port (just let it be for now).
Begin the initial setup sequence. At the appropriate moment, setup assistant will ask if you wish to migrate data from another Mac. At this point, see if it will permit you to migrate apps and accounts.
WARNING: Setup assistant MIGHT NOT WORK, because you are trying to migrate from a "newer" installation back to an "older" one.
If setup assistant won't work, YOU CAN STILL GET BACK, because you have a finder-mountable cloned backup. But you will have to move things slowly, carefully, a little-at-a-time. And don't try this until you do the following:
1. Have the backup drive mounted on the desktop.
2. Click ONE TIME on the drive icon to select it
3. Type command-i (eye) to bring up the get info box
4. At the bottom of get info, click the lock icon and enter your password
5. Now, put a checkmark into "ignore ownership on this volume" to override permissions issues
6. Close get info.
Now you can copy whatever you need from the backup to the new install, and the copied files will "come under the ownership" of your new account.
A lot of work?
YES.
But if you print out and follow these instructions, you CAN successfully "get back to where you once belonged"...
