1. Remove brushed motor.
2. Solder black motor wire to Brushed2Less controller as shown.
3. Attach speed controller as shown.
4. Make and attach Y harness to battery, stock system and brushless speed controller.

A typical battery Y harness will look like the above image. Here is a simple diagram describing what needs to be done:

Your connectors may be different than the image in step 4 above, but the concept is the same as that in the diagram above.

Here is a diagram of the Brushed2Less controller: