Most people think that you need to clean your panels. Really, there is no need unless there’s something significant on them (like a flock of birds have been camped on your system). Dust build up has almost no affect on your production and gets washed off by rain. So, unless you’re really worried about it, there’s no need to get up there.
But if you do want to give them a wash, use clean water (no soap) and try not to get water on the underside of the panels. A quick rinse with a hose should do the trick. Especially remember not to touch the panels if it’s been a sunny day, as they can get up to around 70˚C in a short time.