VBA To Replace One Word In A Cell With Another

I found the below code and have tried adapting it without success.

Code:
Sub Colorize_Word()
Dim Found As Range, FirstFound As String
Dim FindWhat As String, MyColor As Long, Counter As Integer

MyColor = 3

FindWhat = LCase(InputBox("Find what word?", "Color word"))

[Code] ..........

This code finds any string in a cell of your choice and colors it red. I would really like to replace the string with my own string of text. I couldn't use the simple find and replace function as this replaces the WHOLE cell content not just one word.

I believe the line of code that needs editing most is this one

Do
Found.Characters(Counter, Len(FindWhat)).Font.ColorIndex = MyColor
Counter = InStr(Counter + 1, LCase(Found), FindWhat)

But I cannot figure out how to use the replace function with this.