You'll probably get a slew of system updates, one after the other, because it should be up to at least 4.4.4, and 5.0 is currently rolling out. Also make sure all of your apps (including YouTube) are updated in Google Play. Sometimes Google Play won't notify you of an update to a Google app if it has never been updated before (i.e., if it's the original factory-installed app). Search for all of your Google apps on Google Play, and see which ones have an Update button.