OS X Yosemite torrent download link spreads on the web. You can download from Mac App Store also. Sometimes we want one, but sometimes we want go back. I like new OS X Yosemite, but my 2011's MacBook Air is not very good machine for last OS 10.10 Yosemite. OS X Yosemite battery life on my mac is not very good. I want downgrade OS X Yosemite to OS X Mavericks. Yes. It's my business. So bro. If you have such problem or you want go back - you can read this simple guide for downgrade OS X Yosemite to OS X Mavericks:

Step 1: Go to  > Restart and  hold down Command+R to enter Recovery mode;
Step 2: At the OS X Utilities menu, choose “Restore From Time Machine Backup”;
Step 3: Connect the Time Machine drive that contains the most recent Mavericks backup to the Mac (typically through USB or Thunderbolt), then click “Continue”;
Step 4: At the “Select a Backup Source” screen, choose the Time Machine volume used for the Mavericks backup and click Continue;
Step 5: Under “Backup Date & Time”, select the most recent backup made from OS X Mavericks – double-check the OS X Version menu to make sure it’s “10.9.5” (or whatever 10.9.x you had previously), then click Continue again;
Step 6: Choose the Destination drive (the Yosemite volume you want to downgrade) to restore the OS X Mavericks backup to – this will erase OS X Yosemite and revert back to Mavericks on that drive, be sure you backed up all files created between the most recent backup date and now or you will lose them – click on “Restore” to begin the downgrade process.