I'm a big fan of KT controllers. They're user "configurable" to a degree that generally leaves you with a bike set up YOUR way. For instance, when you ask for power, it's there NOW. There's no spool up time. This controller is sold by Bolton as a hop up kit for the RAD bikes. The reason I mention that is that they are VERY popular with those that bought them. There's an endless supply of user reports available.
The KT controllers are available on the after market several ways (don't buy Bolton's kit unless you are working on a Rad), and are generally sold with a new display as part of the deal. Again, there are several displays, all pretty much state of the art, and they are used to set up the controller. Suit yourself. Controller and LCD3 display for instance, should be less than 100 bucks. The controllers are available pre wired with Bafang motor connectors - but make sure you are looking at the RIGHT one! With the correct motor and display connectors assured, you are left matching up the PAS sensor, the throttle, and brake switches. If you understand HAL sensors, this should be a pretty easy job for you.
New controller installed, there is no more bottleneck between the battery and the motor. You MAY be able to get away with the motor you have at that point. It's worth trying. If not, there are 750w and even a 1000w Bafang motors available (buy them pre laced with the correct wheel size - cheap). These will drop right in place where your 500w now lives, and because you've already installed the controller, you'll be able to feed the bigger motors with the amount of power they'll be looking for....
Have fun. Let your wallet be your guide.
