Can i change MAC OS X 10.6 TO MAC OS X 10.9

Welcome to Apple Support Communities

Of course, providing that your Mac supports OS X Yosemite. To check whether your Mac is compatible, open the Mac App Store and try to download OS X Yosemite. If your Mac is not compatible, the Mac App Store will show you an error message.

If you want to upgrade to OS X Yosemite, first you have to make a backup of your files with Time Machine and/or Carbon Copy Cloner on an external drive, so you can restore Snow Leopard if the upgrade goes wrong. Also, as you are upgrading from Snow Leopard, it is quite important to check that all your applications are compatible -> http://www.roaringapps.com

Uninstall or update all unsupported applications before upgrading, so you will prevent future issues. Remember that all PowerPC-based apps will stop working after the upgrade.

What model year is your Mac? It depends on its age - this one can only be upgraded to Lion:

http://www.everymac.com/systems/apple/imac/specs/imac-core-2-duo-2.0-17-inch-spe cs.html

But this one can be upgraded:

http://www.everymac.com/systems/apple/imac/specs/imac-core-2-duo-2.0-20-inch-alu minum-specs.html

Both of them are Core 2 Duos with 2 GHz.

Also, be aware that you will need to add RAM - a minimum of 4 GB is generally recommended.

You are welcome

You will find that any newer OS since Lion runs better with more RAM - you will not be happy with only 3 GB of RAM and neither will your Mac. Make sure you only have one app open at a time; if you do any graphics or video editing, be prepared for long waits to render and/or the beachball. This should be yours - mid 2009:

http://www.everymac.com/systems/apple/imac/specs/imac-core-2-duo-2.0-20-inch-alu minum-early-2009-education-specs.html

It can support 8 GB of RAM and I would highly recommend to do that.

You're welcome - make sure you buy from a recommended vendor offering a lifetime warranty - the two most recommended here are OWC (macsales.com) or Crucial.

http://eshop.macsales.com/shop/memory/iMac/DDR3_2009

Make sure this is the correct one by following their instructions to check your model ID. And, no matter where you get it, get a matching kit of 2 x 4 GB.