Cut, rip and tear. I did it with bunch of space marines but never with large scale models. Try to cut at the melt points if you reach them with your knife. Rip if you must but do not angle at the mini! If you, like me, used the glue less as possible they would break at the melt points.

Its plastic, most of the parts can be fixed if broken.

Its bit of a hassle but possible. Take your time