Assuming that the procedure is the same as on the Galaxy S3, you'll want to open your contacts, tap the menu button (softkey) and tap settings (you may need to swipe through the list, as it's at the bottom). Once in settings, tap "List by" and then select "Last Name"
If you'd also like to have your contacts show up as "Last name, First name" you'll want to repeat the first two steps, then tap "Display Contacts By" and select "Last Name First".
Hope this helps!