You can get away with cleaning out the entire hutch only once or twice a week, but it is highly advisable that you at least clean out the lavatory section of the hutch every single day. Not only will this create a nice environment for your pets to live in, but will also reduce the chances of them contracting nasty diseases such as flystrike.
It's important to clean your rabbits' hutch on a regular basis, particularly in the summer
Rabbits are generally rather clean creatures and will choose 1 or 2 dedicated toilet areas which they will stick to. This makes the cleaning process a whole lot easier as all you need to do is sweep the droppings out and throw them away.
As for the rest of the hutch, it will be a good idea to change the lining and bedding once or twice a week if you have two rabbits. If you have very young rabbits you will need to change the bedding daily.