Changing the time signature

Activate the  tools panel (using the mouse or the Alt+N hotkey).
Press the arrow on the select “Time signature” button “Time signature” button  and set the desired time signature in the opened window.
Move the mouse cursor over the desired position in the staff and press the left mouse button.

All measures from the current measure to the end of the staff or to the next time signature will recalculate to the new time signature.