Try this first (it's easier)
Follow these instructions from Apple: https://support.apple.com/en-us/HT204088
If that won't work for you (possibly because your version of iOS is older)
You can get to your iTunes purchase history from the iTunes application installed on your computer. (It must be the application on your computer, not the app on your device.)
- From the iTunes main menu, choose either Account >> View Account or Store >> View Account. (Some versions of iTunes have one and some have the other.)
- You may have to first choose Store >> Sign In or Account >> Sign In and sign in if the View Account option is not visible.
- On the Account Information screen, find the Purchase History section and click "See All".
- On the Purchase History screen, the upper section will show information on your most recent purchases, and the lower section will show information on older purchases (you may have to use the Previous and Next buttons to navigate to find the appropriate record). Often multiple items are bundled together into a single purchase order, so click on the little arrow to get the items broken out individually.