develop vs upgrade

develop

verb
  • To change with a specific direction, progress. 

  • To progress through a sequence of stages. 

  • To bring out images latent in photographic film. 

  • To advance; to further; to promote the growth of. 

  • To acquire something usually over a period of time. 

  • To place one's pieces actively. 

  • To create. 

  • To cause a ball to become more open and available to be played on later. Usually by moving it away from the cushion, or by opening a pack. 

  • To change the form of (an algebraic expression, etc.) by executing certain indicated operations without changing the value. 

upgrade

verb
  • To replace with something better. 

  • To improve, usually applied to technology, generally by complete replacement of one or more components 

  • To improve the equipment or furnishings of or services rendered to 

  • To replace a program with a later version of itself, a version having a higher version number or marketed under a more recent product name. 

  • To improve in condition or status. 

noun
  • An upward grade or slope. 

  • An improvement 

  • An improved component or replacement item, usually applied to technology 

adv
  • Up a slope or grade. 

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