Sorry, this is not possible. Neither a tourist nor a business visa can be extended.
If you happen to overstay your visa, you will need an exit visa in order to leave the country. An exit visa is to be taken care of by the invitation issuer. Please do not waste time trying to contact any other entities and do not let any information obtained by hearsay influence your actions. Please contact us once you realize that you are unable to leave Russia in time and we will provide detailed instructions as to the paperwork you will have to collect in order to obtain an exit visa.
We find it our duty to warn you that the exit visa obtaining procedure is extremely complicated, time-consuming, and, truth to tell, expensive. We strongly recommend you to avoid overstaying your visa.