*** Upgrading to Yosemite is a fairly simple process. The following is for anyone that wishes to do a clean install of Yosemite. If you want to upgrade over Mavericks, download the Yosemite file from the MAS. It downloads to the Applications folder. When it is finished, double click it and it will start the upgrade process.
1) Backup your computer using Time Machine, Clear Copy Cloner, or SuperDuper
2) Download Yosemite from the MAS
3) The file downloads to your applications folder. Once it finishes, it will want to start the install process. Exit out of the install
4) Make a USB Yosemite installer. You need a 8 GB USB drive and about 20 minutes. The directions are very easy and can be found
here.
5) Once you have the USB installer made, restart your computer and hold down the Command and R button at the same time. Once you see the progress bar start, you can release.
6) Your system will boot into Disk Utility. You want to You want to focus on the bottom option on the screen, because you want to erase your HDD. Erase your HDD and exit out of Disk Utility.
7) Reboot your machine while holding down the option button. The screen that follows will show your Macintosh HD and your newly created Yosemite USB installer options. Click on the Yosemite option. This will start the installation process.
8) During the Yosemite installation, the option to enable FileVault is already checked by default. If you don't want to use FileVault, make sure you uncheck that box.
** You don't have to create a USB installer if you want to upgrade over Mavericks. You can simply download the Yosemite installer as noted before, and then double click it in the Applications folder. That will start the upgrade process. If something goes awry during the install, you will have to download the Yosemite file again, as it gets deleted during install. The method I outlined if for anyone that wishes to do a clean install of the OS.