Delete part of a solid

Hey guys,

is there a way to only delete part of a solid? Which means only part of a solids geometry. Unfortunately my model neither has a surface, nor lines. Only solid.
If that's not possible, is there way to 'reverse transform' a solid into a surface and subsequently a surface into lines?

Of Course remodelling the whole model from the very begining starting with the 1D level would work, but I'd like to avoid that.

Kind regards,
Niclas