Q: Hello is it possible to upgrade OS X Mavericks 10.9.2 when i have Mac OS X 10.7.4???

To install Mavericks, you need one of these Macs:

• 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),
• MacBook Pro (15-inch or 17-inch, Mid/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)

Your Mac also needs:

• OS X Mountain Lion, Lion, or Snow Leopard v10.6.8 already installed
• 2 GB or more of memory
• 8 GB or more of available space

Nevermind.

I found your MBA specs.

It's a mid 2011 model.

So, you are good to go to being able to upgrade to OS X 10.9 Mavericks.

Before attempting any major system upgrade/update, you should have a complete backup of your previous working system and important data just in case something goes wrong with the installation of the upgrade/update and in case you decide you do not like the upgrade/update, you can easily revert to your previous system setup with minimal downtime.

Why are you unable to upgrade through the App Store?

Pete

Anna Dominik wrote:

 

2-what happens if i back up my pc with an external HD, i delete a document in pc and later do another back up?will the document remain my HD or disappear during the last back up?

Yes,

If you delete anything off of your Mac's hard drive and then later do another backup to the external drive, those delete data will be gone on the later backup, too.

If your deleted data is still on the external drive on a previous backup, you can restore this data back from the ext. drive back to your Mac's internal drive before you initiate another more recent backup, though.

Is there some reason you haven't updated your version of Lion to 10.7.5?

Simply click the Apple logo and select "Software update"

Anna Dominik wrote:

 

ohh i see.. and why can't i open my external HD on another computer like WINDOWS ?is it because i usually back up my macbook with it?

It maybe because the hard drive is formatted as a Mac OS X Extended formatted drive.

WIndows will not see or mount the drive.