If the option is available, forced induction (turbocharge or supercharge the engine). Otherwise, basic bolt-ons (air intake, headers, exhaust) can increase hp/tq, but generally the increases are quite minimal.
Got the carpet back in and one door done and tuned. Must say it's pretty loud and clear. Could hear it from in the garage with the door closed down my 150 foot driveway lol I'll do a video once all done No amps visible! Success!
Also if you search our Mazda5 Forum, you should find more info regarding increasing the Mazda5's power output.
Good luck and at the very least, it's worth exploring options.