I would like to make a macro to help me go through 10,000 rows of an excel
spreadsheet.

I have columns set-up with last_name, first_name, address (etc). I would
like to take the first name from one row and add it into the first_name cell
of another row.

Example

John | Doe
Jane | Doe

What I would like to have is:

John & Jane | Doe

Any help??