Would like to uninstall Yosemite (or, YUCKsemite), PLEASE!

Question

I had my 2010 MacBook Pro to the Apple store for a Safari issue. Of course, I could not get the issue to replicate while at the store, but, after discussing my problem with a Genius, he recommended I "upgrade" (I say THAT lightly) to Yosemite. I had been running Mountain Lion, very happily, and was ready to install Mavericks, very happily.
Now, after the "upgrade), my whole computer is running slowly, the Safari issue I took the computer in for has been resolved, but now, it hangs, presents gray screens, and is S L O W.
I am NOT fond of the interface, either. YUCK! Um, Apple, WHY?????? If I wanted to work on a Windows machine, I'd do so.
Any way, I'd like a thorough walk-through, please, of how to go back to Mountain Lion, then install Mavericks, or, if it can be done, just get rid of Yucksemite, and install Mavericks. Links to a step-by-step are fine.
Sorry for the upset rant, but, REALLY! I have been a proud user of Mac since my husband converted me, but now...

Answer 1

Well, I'll prepare you by saying you will have to erase your disk in order to downgrade. Then you will need to be able to re-download the version of OS X you want to install. You will need to reinstall the original version of OS X that came with your computer - 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. Be sure you configure your initial admin account with the exact same
         username and password that you used on your old drive. 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. Now log into the App Store with your Apple ID and password. Click on the Purchase icon in the toolbar. Scroll down your list of downloads until you find Mountain Lion. Click on the Download/Install button. I recommend you also read this:
Make Your Own Mavericks, Mountain/Lion Installer
After downloading the installer you must first save the Install Mac OS X application. After the installer downloads DO NOT click on the Install button. Go to your Applications folder and make a copy of the installer. Move the copy into your Downloads folder. Now you can click on the Install button. You must do this because the installer deletes itself automatically when it finishes installing.
   2. Get a USB flash drive that is at least 8 GBs. Prep this flash drive as follows:
Open Disk Utility in your Utilities folder.
After DU loads select your flash drive (this is the entry with the mfgr.'s ID and size) from the leftside list. Under the Volume Scheme heading set the number of partitions from the drop down menu to one. Set the format type to Mac OS Extended (Journaled.) Click on the Options button, set the partition scheme to GUID then click on the OK button. Click on the Partition button and wait until the process has completed.
Select the volume you just created (this is the sub-entry under the drive entry) from the left side list.
Click on the Erase tab in the DU main window.
Set the format type to Mac OS Extended (Journaled.) Click on the Options button, check the button for Zero Data and click on OK to return to the Erase window.
Click on the Erase button. The format process can take up to an hour depending upon the flash drive size.
Use DiskMaker X to put your installer clone onto the USB flash drive.
Wait for the process to complete which will take quite some time.