decrease vs step up

decrease

verb
  • Of a quantity, to become smaller. 

  • To make (a quantity) smaller. 

noun
  • A reduction in the number of stitches, usually accomplished by suspending the stitch to be decreased from another existing stitch or by knitting it together with another stitch. See Decrease (knitting). 

  • An amount by which a quantity is decreased. 

step up

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

  • To assume or take responsibility. 

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