bump up vs step up

bump up

verb
  • To increase something suddenly. 

  • To promote a person to a higher grade. 

  • To give a more prominent place to; to advance position in queue. 

step up

verb
  • To increase, augment, or advance, especially by one or more steps. 

  • To assume or take responsibility. 

How often have the words bump up and step up occurred in a corpus of books? (source: Google Ngram Viewer )