how can I upgrade my 36v 500w brushless motor to run at 48v

I looked up for information, I couldn't find anything, I hope someone that has experience could help me. I bought the kit on ebay about few months ago, at first the bike was fast enough however when I got used to the speed it feels like it's really slow, and it gets even slower when commuting longer distance.
some of the suggestions online is that I used a 48v batter on 36v controller to run 36v 500w brushless motor, I am hesitant to try this, has anyone tried this before? does it burn the controller or the motor?
other suggestions is to buy a 48v 500 controller+ use 48v battery and use it on my 36v 500w brushless motor to get more power, has anyone tried this? does it burn the motor? any suggestions?

I have a 24v bafang motor, with a 36v controller and used 24v & 36v sla, then switch to 6s Lifepo3(43v) and again I switch to Lipo 12s2p(48v) and loving it. no modification to motor or controller(50v max).

Most likely yes your controller will handle 48 volts. I am personally running two bikes with 36 volt controllers on 48V batteries. If you want to be a little more sure before you try it you can open the controller and read the max voltage printed on the capacitors. If they are rated at 67 volts it should be safe.
The motor just gets happier the more volts you give it until it overheats and smokes or the magnets get too hot and loose strength. Neither of these is likely at 48 volts with responsible use. Get off and put yout hand on the motor after climbing a hill or two. If it gets too hot to touch, you need to take it easy and not work it quite so hard.
48 volts is much more satisfying than 36, especially if you loose 20 pounds or so of lead when you make the switch.

Wow I have pretty much the same question.
My hub motor says 36 volt, but I always assumed it was stamped that way because it shipped as a 36 volt kit.

Are 9c motors actually wired for a certain voltage? I thought all that was determined by the controller and the battery. Obviously I'm not saying that the motor could handle any voltage, but could twelve more volts really make any difference other than speed?

There is about a 99% chance that your 36v controller will work just fine on 48v. To be sure, open the case, look for little cans inside marked 63v. Typical is 63v, not 67.

Add another 12v battery to your existing battery, connect it in series, and you will run 48v. Expect about 4 mph more speed.

It shouldn't fry anything. Once in a blue moon, a controller will pop a cap when you go to 48v, but only because the cap was a defect. The motor will be fine. Adding 12v more won't overcook it. Adding more amps could, but more volts will not likely harm the motor.

The wiring in the E-bikekit dd motors can handle 2000w just fine. So 72v 30 amps, 48v 40 amps, etc.

Motors don't have a set voltage. Even though they might have 36v stamped on them, you can run them at whatever volts you want. As Dogman points out it's the total power that can damage the motor, so going from 36v 20 amps to 48v with the same controller will increase power consumption from 36 x 20 to 48 x 20 watts or 720 to 960 watts. It should be able to handle that, but if you go to say 100v, that would be 2000w, so you would need to cut the current to about 8 amps.

The next thing you need to think about is the efficiency of the motor. If you increase the voltage too far, the motor will want to spin fast, but won't have the torque to reach that speed. If you're at full throttle and the motor is spinning at less than half it's maximum speed, it'll heat up rapidly. There'fore you can't take a small motor, give it 100v and expect to go 40mph. A 33% increase in voltage should be OK for most motors.

Many places that you can buy controllers from also stock controllers. If you buy from China, it would be worth buying a 48v controller at the same time because the additional cost isn't much. Then you can be sure that everything will work.

Right, but it's difficult for us to explain, especially if we are not engineers ourselves.

Typical direct drive motors in bike hubmotor kits tend to be good for up to about 1500w pretty reliable. What voltage you run doesn't matter so much. 72v 20 amps, 48v 30 amps, 36v 40 amps, all are about 1500w. The motor can be run at much higher wattage, and 3000w is very common. But at that wattage, you do tend to get a motor that heats up fast, so you must reduce the duration of the ride to avoid a meltdown. And even then, half way through the ride performance drops as the motor gets too hot.

The main difference in motor rating may just be that if the designers intended to run less than 500w, they will have used thin power wires. The thin wires may not carry 3000w, if you are heading there. So you see wire upgrade threads.

The other thing that really affects motors is the winding. Fast windings make more heat starting up, but reach a faster top speed at a given voltage. A fast winding will also have a faster minimum rpm. Give a motor full throttle, on a hill that slows rpm enough, and it makes tons of heat. So a slow motor tends to climb a hill slower, but with less motor heating.