Looks like Samsung updated it to 5.0, however it could depend if your carrier also decided to update it.
On most phones go to Settings --> System Updates. Pressing System Updates will cause your phone to check for new updates. If there's an update available it will notify you and ask to install OTA.
Or...
Installing a different version of Android yourself requires putting whats called a custom ROM onto your phone/tablet. The custom ROM has to be made specifically for your device, unfortunately you can't simply download any version of Android.
You can put a custom ROM on the phone after rooting it, check the rooting section for your phone for more info:
Note 3 root:
http://androidforums.com/forums/3108
Here is more information about rooting:
http://androidforums.com/threads/rooting-best-practices.450904/
http://androidforums.com/threads/root-terminology.443075/
http://androidforums.com/threads/youve-went-and-rooted-the-phone-now-what.617220/