Hello Ivaylo,
Thank you for posting your issue on Microsoft Community Forum.
I appreciate your concern towards maintaining your keyboard. Though your issue is not technical and that Microsoft does not provide any cleaning kits with the keyboards, I can certainly help you to locate a few instructions and guidelines on the usage and cleaning of the Microsoft Sculpt Keyboard. You may download the product guidein the following link and refer to the steps under usage and cleaning:
Microsoft Sculpt Comfort Keyboard
http://www.microsoft.com/hardware/en-in/d/sculpt-comfort-keyboard
In addition to that, you may search with your favorite search engine for various cleaning kits online, applicable for the keyboard hardware.
I hope this information is helpful. Please feel free to post, in case you face any other issues with Windows in future. We'll be more than happy to assist you.