Vi: Search and Replace
Change to normal mode with <ESC>.
Search (Wraped around at end of file):
 
Search STRING forward :   / STRING.
Search STRING backward:   ? STRING.
 
Repeat search:   n
Repeat search in opposite direction:  N  (SHIFT-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