First of all go to the Mac Store and check , here if you are eligible for the free upgrade. Then check the compatibility of your Mac for installing Mountain Lion , here. Consider that it is recommended that you have at least 4GB of RAM on your Mac, even though officially the system requirements for OS X Mountain Lion are for a minimum of 2GB. The new operating system is not available on DVD and USB stick. In fact, Mountain Lion automatically creates an emergency partition on the computer's memory, saving a backup copy and making reinstallation possible under any condition.
Remember, before proceeding with the installation, to back up everything, possibly with Time Machine and take the opportunity to do some cleaning on your Mac and your applications, using one of the available software such as eg. AppZapper. Above all, those who have previously installed the Lion version and have experienced various compatibility problems with applications such as Office (created by the continuous checks and queries that it proceeds to do as iOS), should consider a preventive uninstallation of these applications and subsequent reinstallation of the latest versions. All these little problems should be solved with the Mountain Lion.
To check the installed version of all other applications, you should access the "Software Update" function of your Mac by clicking on the Apple logo on the top left of your display.
With the release of Mountain Lion, Apple extends some successful features of the iOS mobile world to Macs: first of all, iMessage. Currently available only for iPhone, iPad and iPod Touch, the messaging system supports competitor messengers and also introduces the ability to synchronize conversations between devices, so you can continue a chat on different devices. The inclusion of the Notification Center: alerts appear at the top right and can be configured like on iOS. On the Mac, Notes, Reminders, Game Center, Share Sheets, AirPlay Mirroring, Twitter integration into the operating system are also integrated, iCloud becomes standard and, in my opinion, the function is very useful Share, which, as Apple's website states, “It's the new and simple way to share content directly from the app you're using. Send photos, videos and other files with Mail, Messages and AirDrop. Send links from Safari. And share everything that comes to your mind by posting directly to Facebook, Twitter, Flickr or Vimeo in just a few clicks.” The illustration of all the Mountain Lion news can be found at: http://www.apple.com/it/osx/whats-new/
Speaking of security, Mountain Lion contains the feature Gatekeepers, which allows users to decide the minimum certificates for installing applications: the initial settings allow downloading only from the Mac App Store and official developers, but you can also decide to approve less certified sources.
