Upgrade (stress on "e") is a software or hardware upgrade to a more modern version. The word upgrade can be translated from English as "transition to the next class". And in fact, nefig linger on Windows 7 in 2015, it's time to upgrade your axis to "dozens"!
The upgrade can be considered a synonym for the update , but there are also nuances. The update, as a rule, means a small update, while an upgrade is a more serious upgrade, where you will need much more time, money and savvy.