VBA macro Excel : I've never done macros before so please bear with me while I try to explain what I want to accomplish:

I have a sheet that has some `names` and `SSN's` and then has 4 columns filled with the following values: `S`, `MB`, `B`.

For said columns I wish to replace `S` with the number `4`, `MB` with the number 3 and `B` with the number 2. I have thousands of excel files that will need this change and doing it manually with a `CTRL+F` and replacing for each excel sheet is not going to cut it, timewise. 

Can anyone get me started on how to accomplish this?