How to search and replace in vi editor

Change to normal mode with ESC

Search

Search STRING forward   /STRING

Search STRING backward  ?STRING

Search next   n

Search previous  N

Replace

Same as with sed, Replace OLD with NEW

First occurrence on current line      :s/OLD/NEW

Globally (all) on current line:        :s/OLD/NEW/g

Between two lines #,#:                 :#,#s/OLD/NEW/g

Every occurrence in file:              :%s/OLD/NEW/g