You can improve the capability, if you know the weak links and how to upgrade, but you cannot change the rating. Only a manufacurer can change the ratings.
Where to start on upgrades, depends on the truck. Sometimes weak point is tire and wheels, sometimes cooling ssystem, sometimes suspension parts, sometimes powere steering gear, somstimes axle capacities, sometimes limits on transmissions.
People get focused on power, which is the least likely problem, since most modern pickups, SUVs, even minivans, have more power than trucks 10-20 years ago that pulled 2 to 5 times what our light vehicles are rated to tow today.