Before returning it try wiping the cache partition. If that doesn't help, I would try a factory reset.
Here are the instructions for a factory reset from recovery:
- If your phone is on, turn it off.
- Press and hold the Volume Down and Volume Up buttons, and then press and hold the Power button at the same time until the phone turns on. You'll see the word "Start" with an arrow around it.
- Press the Volume Down button twice to highlight "Recovery mode."
- Press the Power button to start Recovery mode. You'll see an image of an Android robot with a red exclamation mark and the words "No command."
- While holding the Power button, tap the Volume Up button once.
- Use the volume buttons to scroll to "wipe data/factory reset" and press the Power button to select it.
- Scroll down to "Yes - erase all user data" and press the Power button to select it.
To wipe the cache, follow the same steps but choose the wipe cache option instead of the factory reset option. Wiping cache will not cause you to lose any data, but a factory reset will. Make sure you back up any important pictures, texts, etc. before performing a factory reset.