Can I update from OS X 6.8 to El Capitan?

Yes, if your Mac’s compatible with it.

(136786)

That depends entirely on the model of Mac. If your Mac supports el Capitan then yes.

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

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)

No such thing as a 21 inch MacBook Pro. 13, 15 or 17 inch at most.

21" is only for desktop iMacs.

You can look in the Apple Menu->About this Mac, for the specific model, year, and type of Mac.

Hello I see you need help updating your mac.

Here is some help.

If your Mac is running Snow Leopard (v10.6.8) or later, you can upgrade directly to El Capitan.

General Requirements

• OS X v10.6.8 or later
• 2GB of memory
• 8.8GB of available storage
• Some features require an Apple ID; terms apply.
• Some features require a compatible Internet service provider; fees may apply.

iMac: Mid 2007 or newer MacBook: Aluminium Late 2008; Early 2009 or newer MacBook Air: Late 2008 or newer MacBook Pro: 13-inch, Mid 2009 or newer; 15-inch, Mid/Late 2007 or newer; 17-inch, Late 2007 or newer[21] Mac Mini: Early 2009 or newer Mac Pro: Early 2008 or newer Xserve: Early 2009 These computers support features such as Handoff, Instant Hotspot, AirDrop between Mac computers and iOS devices, as well as the new Metal API: iMac: Late 2012 or newer MacBook (Retina): Early 2015 or newer MacBook Air: Mid 2012 or newer MacBook Pro: Mid 2012 or newer Mac Mini: Late 2012 or newer Mac Pro: Late 2013 or newer The upgrade will download and use around 6 GB of disk space. You will need a newer mac

You also might want to check your macs hardware

I will not recommend you updating to OS X 10.11 Your Mac might run very slow.

🙂

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

You will also need to add more RAM - a general recommendation is a minimum 4 GB of RAM, but that is enough to browse the internet and if you do some word processing, you should consider more for any photo or video editing or your experience will not be very satisfying.