I don't know how to do what you want, but <Ctrl><Alt><F9> will update
it.

I believe that with Excel (from Excel 2000 onwards), this can be done
in VBA with the command
Application.CalculateFull

I tried Application.Calculate and the code runs without error but
doesn't update  the function. With Application.CalculateFull the
function returns  Value error.

Was told that I need to use class modules but I don't know what it is
so I need to read up on it to figure out a way.

Another option would be to have a macro which replaces all incidences
of an equals sign with an equals sign using something like:

Cells.Replace What:="=", Replacement:="=", LookAt:=xlPart

This forces each cell with a function  to be changed and then
calculated.
You'll need to decide if you want to do all the sheets in the
workbook.