Transfer is easy.
1: Choose a registrar where you would like the .eu domain to reside and request the domain from there control panel. Sometimes you can request the domain from the control panel even if the domain is already registered. Then automaticly the request for transfer or trade will be put in place
If this can not be done you have to call the sales department or other type of support and ask them to request a ''trade'' or ''transfer''.
Then this registrar will put the request in at Eurid and Eurid will recognize the domain is already registered to someone else and sends a confirmation email to the current owner for transfer of ownership.
The current owner will be directed to the website of Eurid where the confirmation is waiting for him. He needs to enter a verification code and check a few check boxes and confirm.
That's it! The domain will be transferred to the new owner or the same owner but now with another registrar or to another person within the network of the same registrar.
You can check this
link to view the explanation of Eurid.
It's basicly the same as the above.
I do believe a €10 transfer fee is involved but i don't know if this is the same for a trade...the domain changing ownership within the network of the registrar where a .eu domain would currently reside.