Clean them from what LARCH?
Green algae and moss can be removed with the appropriate Brand solution from your local DIY store.
If they are concrete pavers and you have that 'white' stuff appearing on top, this can easily be removed with a solution of half water and half hydrochloric acid. Safety first please!
If it is just normal dust and dirt from BBQs etc., a small pressure washer as mentioned by camioneur is indeed an easy tool to use. Make sure to use a lowish pressure though. It is surprising how easy it is to damage the top layer of pavers with a high pressure sprayer.