To delete the document or phrase you just need to swipe it off the main screen (list of documents or phrases) to the left for the red DELETE button to appear on the right side. Push DELETE and the document or phrase will disappear from the list and the library. This feature is common for the whole iOS system and can be used in most of the scroll lists through apps.
Please follow this link from Apple for help on setting up the wallpeper:
https://support.apple.com/en-us/HT200285
Make sure not to implement BLUR option for best results.