Replacing Drive shaft on Climax

[2foot6]

OK all the experts out there,I have just tried to replace the drive shaft on the bogie of a Climax, Bachmann didn't supply the shaft with the square tube,so  I need to remove the old square tube and fit to the new shaft to it.The question is HOW TO REMOVE THE OLD SQUARE TUBE from the ring /universal?  Thanks guys,,,,,,cheers Peter.