On the old Punto, it's just brute force, and a lot of it! Also, try nugging and twisting the knob a bit while you're pulling upwards. I wouldn't suggest doing this several times with the same gear knob (1st time - "it's doable!", 2nd time - "Ahhh, it's looks like this under the knob!", 3rd time - "Let me just get the meashures") because eventually the plastic knob will end up in your palm in the middle of a very important shift down (let's say when you loose traction on a partially wet road, on a bad curve, with trucks, and busses and pedestrians with little children about). If you go for the hacksaw option, be carefull not to cut the metal shaft - it goes a long way into the knob.
