Rear Suspension Upper Ball-Joint Arm

I got the upper arm removed because the ball joint broke, I just noticed the balljoint bolt is welded or pressed in the lower arm. I got a new upper-arm and ball joint but I cant get the broken one out of the lower arm? anyone know how to ? Do I have to heat it up or what?

Mine was rusted to the point that I had to grind off the bolt/nut combo, which was just a rounded mass, could not tell what was bolt, what was nut. Soon as I ground enough off, it popped loose.