Hi Adrienne,
TextToColumns is a built in Excel function which will do this for you.
Just make sure you have a blank column to the right of your column with the names as it will put everything after the space into a column directly to the right of it. Then, highlight the column, go to the Data menu, and under data tools click text to columns. Click delimited and choose space as your delimiter. That should be it!
I also wrote an article on how to do this exact thing if you run into any trouble you could use it for reference or leave another comment below.
http://www.germanpearls.com/excel-text-to-columns-separate-names/
Good luck!
Amy