If the section you're removing is load-bearing — a wall, column, or beam carrying weight from above — that's a job for a professional team with engineering input, not a weekend project.
Any demolition near existing utilities, in an occupied building, or on a shared-wall property line carries risk that's easy to underestimate until something goes wrong.
As a general guide: non-structural, isolated, ground-level concrete is often manageable independently. Anything load-bearing, anything near utilities, and anything in a shared or occupied building is worth bringing in a professional demolition team for.