Changing the dictionary of aruco in aruco_ros package

I am using Logitech C270 with resolution 640x480 to detect aruco marker using aruco_ros package. I have succeeded to detect the marker when the distance between the marker and the camera is 180 cm. But I want to detect the marker when the distance between the marker and the camera is 240 cm. The marker which i used it from the dictionary 6x6. I tried with marker 5x5 but i failed. I think that when I can change the default dictionary from 6x6 to 4x4 I can solve this problem. I need help in changing the dictionary or any other idea assist me, Please.