There are members on this forum that are way way smarter about this stuff than I am. So take my "opinions" with a grain of salt.
If you want to stay at the same speed and the cheapest route, purchase a replacement ECX13010 ESC/RX for your cars. If you want a little room to improve later down the road, this is what I purchased when I jumped from Nimh packs to LiPo's.
I also went deep into the rabbit hole and purchased Zeee 2s LiPo's as well.
I still have both of these, and they are still in one of my Torments, and they do still work, and it's been 1.5-2 years now. I'm not trying to sell you on this combo at all, I did read some reviews before i purchase them, that others have had somewhat lackluster results with them. You mileage may very.
Now keep in mind, your current ECX13010 is a 2-n-1, it houses the ESC and the RX, which is the receiver for your Transmitter (radio), on top of moving to the brushless system of your choice, you will also need to find a receiver that will bind and work with your current transmitter. So you will have to research that a bit or post your radio here, I could assume what you have if you purchased it new and it is the stock radio that came with the kit. But I would hate to do that and then lead you down the wrong path.
To end this post, I do want to say, if I had to do it over again, and if you are going to spend time in the hobby for some years, I would/should have went with a more top tier setup at the start, not that I have had problems, but my need for wheelies galore surpassed my initial budget quickly....LOL
I would have spent the extra money and got a Hobbywing, Castle, or Tekin, setup off the bat and had a lot of room for improvements later on. Not only for their reliability, but for their customer service as well. I cant go back to the ebay store I purchased the GoolRc system from if I had a issue outside the 30 days? But again, I shouldn't tell you what you should do, just offer you my experience.