The cleaning instructions should have come with the furniture but if they're lost or forgotten...
You can clean it well using the upholstery attachment on a dirt extractor. You can rent or buy them. I own a Hoover dirt extractor and can tell you that it's well worth the cost of buying one. Rentals start at $30 a day, buying a home dirt extractor costs about $100 and up.
The other method is more work but will clean the furniture. Use a good all-purpose cleaner (like Greased Lightning) and a good microfiber cleaning cloth. Just wipe off the dirt and repeat as many times as necessary.
I find that having arm protectors on the furniture greatly reduces the need for cleaning.
