Q: how to upgrade from snow leopard to el capitan

The Appp Store in iTunes is for downloading apps for the iPhone, iPad or iPod not the Mac.

You should have an App Store on you Dock. If you do not check for it in the Applications folders. Use it to download El Capitan.

How to upgrade your OS:

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

Are you sure you are at 10.6.8 as you claimed in your original post?

nonilaz wrote:

 

dont have it in dock or anyway at my mac.......   ;(

As I recall on Snow Leopard the App Store connection was in the main Safari menu.

Click on the  icon in the far left of the menu bar.  From the drop down menu. is there an entry for the App Store?  If so, click on it.

Ciao.

Wikipedia says this about the App Store:

It was released on January 6, 2011, as part of the free Mac OS X 10.6.6 update for all current Snow Leopard users.

I would think that re-running the 10.6.8 combo update (and perhaps also the Supplemental, if you have never applied it), which you can get from from Apple's site, might reinstall the App Store: Apple - Support - Downloads

You might just run Software Update, which you may have turned off long ago.

Apple issued a Mac App Store Update for OS X Snow Leopard in January 2016. See About the Mac App Store Update for OS X Snow Leopard - Apple Support

Check to make sure your applications are compatible. PowerPC applications are no longer supported after 10.6.      

Application Compatibility

Applications Compatibility (2)

El Capitan 10.11 Compatibility information

Do a backup before installing, preferable 2 backups on 2 different drives.