How do I replace all cell references with another one when they appear multiple times in an expression?

[FSAEStudent]

For example here is the expression i got:
=(IF(((4*F4*F5*J5*J8*J11*J15*((F10/2)+(F11/F9)))/(F10*F18*B10))<=((B7+B15+(4*B5*B9*F4*F5/(B5*B8*B10)*(((J5*J8*J11*J15*((F10/2)+(F11/F9)))/(F10*F18))+(K5*K8*K11*K15*((F10/2)-(F11/F9))/(F10*G18)))))*B12),((4*F4*F5*J5*J8*J11*J15*((F10/2)+(F11/F9)))/(F10*F18*B10)),(IF(((4*F4*F5*J5*J8*J11*J15*((F10/2)+(F11/F9)))/(F10*F18*B10))<=((B7+B15+(4*B5*B9*F4*F5/(B5*B8*B10)*(((J5*J8*J11*J15*((F10/2)+(F11/F9)))/(F10*F18))+(K5*K8*K11*K15*((F10/2)-(F11/F9))/(F10*G18)))))*B12),0,(B7+B15+(4*B5*B9*F4*F5/(B5*B8*B10)*(((J5*J8*J11*J15*((F10/2)+(F11/F9)))/(F10*F18))+(K5*K8*K11*K15*((F10/2)-(F11/F9))/(F10*G18)))))*B11)))+IF((4*F4*F5*K5*K8*K11*K15*((F10/2)-(F11/F9))/(B10*F10*G18))<=((C7+C15-(4*B5*B9*F4*F5/(B5*B8*B10)*(((J5*J8*J11*J15*((F10/2)+(F11/F9)))/(F10*F18))+(K5*K8*K11*K15*((F10/2)-(F11/F9))/(F10*G18)))))*C12),(4*F4*F5*K5*K8*K11*K15*((F10/2)-(F11/F9))/(B10*F10*G18)),(IF((4*F4*F5*K5*K8*K11*K15*((F10/2)-(F11/F9))/(B10*F10*G18))<=((C7+C15-(4*B5*B9*F4*F5/(B5*B8*B10)*(((J5*J8*J11*J15*((F10/2)+(F11/F9)))/(F10*F18))+(K5*K8*K11*K15*((F10/2)-(F11/F9))/(F10*G18)))))*C12),0,(C7+C15-(4*B5*B9*F4*F5/(B5*B8*B10)*(((J5*J8*J11*J15*((F10/2)+(F11/F9)))/(F10*F18))+(K5*K8*K11*K15*((F10/2)-(F11/F9))/(F10*G18)))))*C11))))/B5

I need to replace all the cell references of "F4" to "O$3" in one action, how do I do this?

 

[Fluff]

Hi & welcome to MrExcel.
Select the cell with the formula & use the Replace function (Ctrl H) put F4 in the Find box & O$3 in the Replace box.
Then in options make sure that "Match entire cell" is unchecked & "Look in" is set to Formulas
Then click "Replace"