The invention relates to a method for modernizing a multiroll calender, which multiroll calender is for calendering a fiber web, particularly a paper or board web (W), which multiroll calender comprises at least one stack of calender rolls (10, 20), each stack comprising at least two calender rolls (11, 12, 13, 14, 21, 22, 23, 24) and at least one of the calender rolls is a smooth-surfaced press-roll (12, 22). In an existing multiroll calender at least one smooth-surfaced press roll (12, 22) is replaced by an ultra thermo roll that is a thermo roll diameter of which is substantially the same or less than the diameter of the thermo roll to be replaced, surface temperature of the ultra thermo roll when heated is at least110 °C, at least 10 °C higher surface temperature than surface temperature of rolls of prior art with same heating fluid temperature and having flow channels arranged in such way that the vibration excitation is minimized, advantageously arranged to form a spiral shaped geometry in the mantle.