Pre 2001 petrols generally are mappable via the diagnostic port. You can use a piggy back ECU to change the control parameters. Alternatively the traditional 'chip' change is a good option. This where the new map is burned to an EPROM and it's then soldered into the circuit board in place of the original one. Alternatively it might be a DIL socket so therefore no soldering.
What you won't though is an extra 50bhp. The most you'll see is about 10bhp, and mostly at the top end of the rev range. The new control data will smooth the torque curve lower down so the car will probably feel faster even though the net increase isn't all that great.