This is a very common function when performing string manipulation… you simply pass in a character or string that you wish SQL to look for, the text in which to look, and what you want the character or string replacing with.
Character replace
declare @text varchar(40)
set @text = 'mom'
select replace(@text, 'm', 'b')
String replace
declare @text varchar(40)
set @text = 'flash'
select replace(@text, 'la', 'i')