How to show actual formulas in cells and can I use find/replace to change a series of valu

Hello. How would I show actual formulas in cells and can I use find/replace to change a series of values within the formulas then switch the view back.
e.g.

Result = 4
Formula = =sum(a1:a6)
Action = I want to replace a with column h, therefore formula =sum(h1:h6)