Need help with swapping the front wheels on a Plarail chassis

Hey guys, I'm new on here and was hoping to get help with something. (Hope it's ok to post the thread here BTW)

I'm ordering a Plarail Thomas and Merlin Coal Hopper set, I'm hoping to make the Merlin from the set Motorized and I have a spare 2015 Plarail Gordon Chassis to achieve this. I was going to swap the wheels and give the motorized chassis Merlins red wheels.

However a problem has occurred, I can't seem to remove the front wheels from the axle. It seems on one side the front axle might have been screwed really tightly or it has permanently been pined together. 

I was wondering if anyone has had any experience with this issue and also have solutions or ideas on how to remove the front axle and swap the front wheels.

Thanks