Swaping and merging two columns

[brownh hartford-hwp com (Haines Brown)]

I have a worksheet set up so that the first column is LastName, the
second column is FirstNamd, and the next two columns hold the
address. 

This arrangement is convenient for entering data, but now I want to
export the data as CSV in order to print labels with glabel. 

However, to do that I need to reverse and combine the data in the
first two colums so that it becomes one column with its cells holding
"FirstName Lastname". Any copy/pasting or merging I try overwrites the 
data in the target cell rather than append to it.

What to do?

Haines Brown