One of the major reasons behind a slow performing iOS device can be the old iOS version it is using. Using an old iOS version can also sometimes make your iPhone, iPod or iPod touch behave weird and can be easily rectified by updating the software. iOS can be updated to its latest version either wirelessly or using iTunes.
Irrespective of the method used, it is always recommended to back up your device before updating.
If a software update is available to your iOS, you may get a message directly saying that an update is available. Simply tap on the message saying Install Now.
Alternatively, the iOS can be updated with the help of the steps bellow:
Note: If you are having space issues while updating the device wirelessly, you can either update your iPhone using iTunes or you can manually delete some content from your device.
If you are having trouble in updating your device Wirelessly, you can manually update it using iTunes from a computer. Before updating ensure that your computer is connected to your home Wi-Fi or Ethernet.
Both the above-mentioned methods can be used to update your iPhone. In case if you are getting error about low storage space, simply delete content from your device manually.