Replacing your vehicle's catalytic converter isn't quite like replacing a tire you'll need to raise the entire vehicle off of the ground, rather than just one corner. It's very important to find a level spot to do this maintenance on your car. If your car is not stable, you risk serious injury or death if your jacks fail. If you have access to a professional-quality hydraulic lift and know how to safely use it, this is also an acceptable way to lift your car when replacing the catalytic converter. If your vehicle hasn't had an opportunity to cool down after running, its exhaust system can still be quite hot. To reduce the risk of painful burns, give your vehicle a chance to adequately cool down before working on it. Depending on your vehicle's exhaust system, this will usually be a matter of just a few minutes. To test the heat of the exhaust system, put on a pair of heavy mechanic's gloves and gently brush the exhaust tube with the back of your hand. If you can't feel any heat, you may cautiously repeat this test without the glove. Slide under the vehicle and locate the tubes of the exhaust system, which should run all the way to your vehicle's rear exhaust. The converter should not be terribly difficult to find it will usually take the form of a rectangular or rounded "box" in the middle of your exhaust system. Some models can have a roughly cylindrical shape. Check to see whether the converter is bolted or welded to the rest of the exhaust system at its connection points. You may need to take it to an auto shop to have it repaired if it has already been replaced and welded back into position, rather than bolted. You can still replace a welded converter if you have access to a sawzall (or similar tool) and a welding machine and know how to safely use both, but these advanced tools are beyond the mastery of most amateur mechanics. Most modern catalytic converters are equipped with one or more oxygen sensors that monitor the efficiency of the car's exhaust system continuously. If your catalytic converter has an attached oxygen sensor, use an oxygen sensor socket and a ratchet wrench to disconnect it before proceeding. When you're done, move the sensor out of your way so that it doesn't interfere with the rest of the process. Catalytic converters that are bolted in can sometimes have bolts that are rusted, partially-corroded, or "jammed" into their nuts. These bolts can be very tricky to remove, so loosen them up by applying a penetrating oil (available from most auto stores). Allow the oil to seep into the bolts and lubricate them for several minutes before attempting to remove them. Use an appropriately-sized wrench to begin loosening all of the bolts before you start removing them. Once all of the bolts are loosened (but still attached), remove the "rear" bolts (those closest to the open end of the vehicle's exhaust) before removing the "front" ones (those further away). Remove the converter when you're done. You may have to support the exhaust once the converter is removed. If your converter is welded into the rest of the exhaust system, rather than bolted in, the only way to remove it is to physically cut it out of the pipes it's connected to. Most mechanics will use a sawzall or similar tool for this purpose. Cut along (or near) the existing weld lines, then remove the converter after it's cut free. If you finish and the converter won't seem to budge, you may want to use a hammer to knock it out of its place as long as you take care not to damage or rattle any other parts of the exhaust system (this can lead to harmful exhaust leaks down the road).
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One-sentence summary -- Park in a level place and jack the vehicle up at all four wheels and support on jack stands. Allow the vehicle's exhaust to cool down. Locate the catalytic converter. Remove the O2 (oxygen) sensor from the catalytic converter. If bolted, apply penetrating oil to the bolts. Remove the bolts at the back end first, then at the front. Alternatively, for welded-in converters, cut the converter out.

The shocks and springs in the suspension of your car were designed and built with your comfort in mind. In order to maximize comfort, the suspension allows the wheels to move up and down to limit how much the body of the car is affected by bumps. Replacing these components with stiffer shocks and springs will compromise some of your ride comfort, but the added stiffness will keep the tires in contact with the road better, thus improving traction when accelerating, braking, or turning. Coil-Overs are adjustable shocks and springs that allow you to lower the vehicle and stiffen the ride based on your preference and driving style. Many stiffer suspensions also lower the vehicle, which lowers its center of gravity and also serves to improve handling. Anti-roll bars cross the undercarriage of your car at the front and rear to connect the sides of the body and increase the structural rigidity of your car. Swapping out the stock anti-roll bars with larger diameter replacements will increase the rigidity of your car's body even further. This increased stiffness helps to ensure the tires remain as flat as possible on the ground to maintain good traction. When buying anti-roll bars, it's best to purchase them in pairs so the front and back offer the same level of torsional strength and don't permit your car to twist under the torque of hard launches or sharp turns. Anti-roll bars are also referred to as sway bars, anti-sway bars, stabilizer bars or roll bars. High strength tubular steel is often a better alternative to solid bars, which can be extremely heavy. Your suspension has a number of bushings separating moving metal parts, reducing vibrations and helping to maintain your car's weight distribution. Unfortunately, the rubber these bushings are made of tends to break down over time. Polyurethane replacement bushings are much stiffer than their rubber counterparts and won't wear down the way stock ones will. Polyurethane bushings will make loud squeaking noises if not properly greased when installed. Bushings can be replaced one by one or kits can be purchased to replace all of your bushings at once. Some bushings may require the use of a press to remove from their housings. Strut tower bars connect the right and left side of your car in much the same way anti-roll bars do, but they are installed on the top of the car under the hood and trunk lid. These bars directly connect the driver's and passenger's side struts, increasing the structural rigidity of the car and aiding in efforts to keep the tires as flat on the pavement as possible during aggressive driving. These bars make an excellent addition to after-market anti-roll bars to reduce the amount your car leans and twists while turning. You may not be able to access the rear strut towers to install a bar in the back of some cars. Strut tower bars may need to be removed when working on the engine of your car in the future. One could argue that being able to stop is the most important part of any car's performance. The better quality your brakes, the longer you can wait to engage them before a turn, which means maintaining a higher rate of speed longer than your competitors. You have lots of options when it comes to upgrading your brakes, from purchasing better brake pads to replacing the entire system with larger, heavier duty components. Aftermarket brake pads are designed to improve your car's ability to stop. They use the stock brake components and are a great option for most street applications. Different brake pad compounds are designed for different uses. Ask your local auto parts store about the options available for your specific car. Kits can be purchased to replace your car's brake calipers and rotors with larger ones, increasing the friction surface of the brake pad and improving your ability to stop. It's important to ensure your wheels are large enough to clear big brake upgrades.
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One-sentence summary --
Replace your shocks and springs with higher performance alternatives. Install larger anti-roll bars. Swap rubber bushings with polyurethane. Install a strut tower bar. Upgrade your brakes.