iOS version 10.10.0

If you did not already buy Mac OS X 10.10 Yosemite, you missed it. It is no longer available for NEW purchases.

The current version at this writing is 10.11 El Capitan, available only by download, and only by running the [Mac] App Store.app (available in 10.6.8). If you do not have that in your Dock, look in the /Applications folder (where / means starting at top-level).

It is currently on sale in the [Mac] App Store for $0.

Mac OS X is not legitimately available at any Publicly-accessible Web sites, and if you should find a copy, it is extremely likely to come with additional malware added.

When upgrading your Operating System, it is always Prudent to have a Trusted Backup. If you do not have one, you should get an external drive and turn on Time Machine and make a Backup before proceeding.

By design, a Mac Operating System upgrade is intended to change ONLY System Files, and not disturb anything else. It works very conservatively, first by using a new stripped-down version of the incoming Mac OS X to run the Installer, then carefully unpacking new files. as the last step, it moves most files into position, and at the next Restart, finishes moving files into position. If it fails short of the last steps in the process, it is intended to leave your original Operating System unchanged.

Mac Hardware Requirements

For details about your Mac model, click the Apple icon at the top left of your screen, choose About This Mac, then choose More Info. These Mac models are compatible with OS X El Capitan:

• MacBook (Early 2015)
• MacBook (Late 2008 Aluminum, or Early 2009 or newer)
• MacBook Pro (Mid/Late 2007 or newer)
• MacBook Air (Late 2008 or newer)
• Mac mini (Early 2009 or newer)
• iMac (Mid 2007 or newer)
• Mac Pro (Early 2008 or newer)
• Xserve (Early 2009)

from:

http://www.apple.com/osx/how-to-upgrade/#hardware-requirements

There are a lot of weasel-words in my description above, because if something goes wrong, it is entirely possible that everything on your computer could be lost. That is why a Trusted Backup is essential.