From Hlavní Nádraží train station or Nádraží Holešovice train station: Take underground C (Red line) to Florenc station, where you change the line from C (red) to B (yellow), then travel to Náměstí Republiky (1 stop).
Take bus No. 100 from the airport to the terminal metro stop Zličín where you change to the metro Zličín, B line (yellow), then travel to Náměstí Republiky (12 stops).