Are you sure that it is the 5th generation? If it is, then the highest iOS version available should show up when you go to Settings? General > Software Update
Note that that model # would indicate that it is a 4th generation model.
Here is the highest iOS version available for each device.
Maximum iOS Version for iPod, iPhone & iPad @ Everyi.com
iPod touch (4th Gen/FaceTime) iOS 6.1.6*
iPod touch (4th Gen, 2011) iOS 6.1.6*
iPod touch (4th Gen, 2012) iOS 6.1.6*
iPod touch (5th Gen) iOS 9.x
iPod touch (5th Gen, No iSight, 2013) iOS 9.x
iPod touch (5th Gen, 16 GB, 2014) iOS 9.x
iPod touch (6th Gen, 2015) Current