How can I remove lower trailing arm from 1997 (P) Nissan Micra?

I need to replace my rear axle of a 1997 Nissan Micra, to do this the rear trailing arms need to be removed. Both arms, left and right are extremly tighltly bolted and cant be removed as normal, on one side the nut has come of but the bolt will not move even if hammered. How can I remove these parts so that they can be connected to the new axle?