I’ve only got a low-budget workshop (I can’t afford decent tools yet, just wait…) and I removed the most stubborn nut by selecting a spanner that was slightly too small, using the hexagonal grip end, placing it over the nut and then whacking it on with a hammer. Then using the hammer to knock the spanner sideways to undo it.
“There’s no problem in life that can’t be solved with a sufficiently large hammer”.