instructions on how to clean them

I own a pair of white Duvet Moon Boots. I love them, and it is no exaggeration to say that I get a compliment every time I wear them. I knew when I bought them that white is not a practical color, but I chose them anyway because they look so great.
Can you please give me instructions on how to clean them? They are getting dirty from snow sludge.
Many thanks.
Peggy (Dublin, Ireland)