Aha, it sounds like your current ESC is for brushed motor (2 wires), with the other end a pair of wires to battery and triplica wire (small guage & joined) for the RX.
If you upgrade to brushless, it sounds like you would have to go for a new ESC anyway.
Here's a motor that would probably get you moving: http://www.giantshark.co.uk/cf2812-1...otor-p-52.html
This is the 'BlueWonder', but depends on how you can mount it: http://www.giantshark.co.uk/blue-won...-p-404459.html
Another that would help your model move well: http://www.giantshark.co.uk/epower-2...0kv-p-255.html
All brushless, so you need a brushless ESC somewhere around 20A (25A for margin).
I just linked to a site in UK, but look around and see if you can get a supplier more local. I'm sure other RCG-ers may be able to offer guidance where to get the parts you need. HobbyKing are popular in US, expanding into UK so good for me
Which ever motor you get, with brushless power you will have a lot more 'poke' than the old brushed motor of same size.