1. Go into the "Play Store" app.
2. Open the "Menu" on the left.
3. Tap "Settings".
4. Now look for the "User Controls" section and then find and tap "Content Filtering".
5. Change it to the setting you wish and then tap "OK".
Now if that device has been restricted by say parental controls, we can't help with that. You would have to talk to who ever it was that set up the blocking on the device.