Complex sentence: In 2011 company was renamed to "Telefónica Czech Republic" and in 2013 it was announced, that Telefónica will sell its stake in company to PPF and company will continue to use the O2 brand for a maximum of four years.
Split into simpler sentences: In 2011 company was renamed to "Telefónica Czech Republic" and in 2013 it was announced that Telefónica would sell its stake in the company to PPF. Under the terms of the sale, the company will continue trading under the O2 brand for a maximum of four years.