you can change the sleep time:
- tap the menu button at the bottom right (beside the home button)
- system settings
- under general settings select Display
- select sleep
- select the time you want
Under General settings you can also turn wifi on/off and data on/off
- where it says wifi, turn it on/off
- select mobile networks
- make sure data isn't enabled
OR
you should be able to turn wifi and data on/off on one of your home screens.
- there should be a widget on one of home screens that shows buttons like wifi, gps, data, and so on. Slide to that home screen
- the ones that are the brightest are the ones that are on. You can tap on wifi to turn it on or off, and you can tap data to do the same.
hope I explained it right!