my iMAC OS X 10.6.8 cannot upgrade to Lion

Check that you can run mavericks:

Check via Software Update whether any further updates are required, particularly to iTunes (you will need the latest version in order to synch with mobile devices).

You should now see the App Store icon in iTunes, and you now need to set up your account:

http://support.apple.com/kb/HT4479

You can now upgrade to Mavericks OS 10.9 for free IF you have one of the following Macs, with not less than 2GB of RAM, and at least 8GB of available space on your hard drive:

iMac (Mid-2007 or later)

MacBook (13-inch Aluminum, Late 2008), (13-inch, Early 2009 or later)

MacBook Pro (13-inch, Mid-2009 or later), (15-inch, Mid/Late 2007 or later), (17-inch, Late 2007 or later)

MacBook Air (Late 2008 or later)

Mac Mini (Early 2009 or later)

Mac Pro (Early 2008 or later)

Xserve (Early 2009)

iCloud system requirements:

http://support.apple.com/kb/ht4759

If you cannot run Mavericks you can purchase the code to use to download Lion from the App Store (Lion requires an Intel-based Mac with a Core 2 Duo, i3, i5, i7 or Xeon processor and 2GB of RAM, running the latest version of Snow Leopard):

http://store.apple.com/us/product/D6106Z/A/os-x-lion

or Mountain Lion:

http://store.apple.com/us/product/D6377Z/A/os-x-mountain-lion

Apple has removed both Mavericks and Yosemite from the App Store.

You have to purchase Lion from the Apple online store, not the App store:

http://www.apple.com/shop/product/D6106Z/A/os-x-lion

Ciao.

Yes, you have to buy Lion, and you should upgrade your RAM to the maximum 3 Gigs.

http://www.apple.com/shop/product/D6106Z/A/os-x-lion

However, I would recommend sticking with Snow Leopard, and upgrading the RAM to 3 Gigs. Your iMac is 9 ½ years old and OS X Lion is probably one of the least popular OS X versions.