By the bad quality of 370 motor in 1:18 Volcano, I want to convert the Brushed system to Brushless. But I'm newbie so need some help

1/. Can I keep the Transmitter and just replace the Receiver (save alot of money ) ? - If can, which Rx can Compatible which this Tx
2/. Do The Servo & Battery need to change ?

Thanks for all

I am 90% sure you will have to replace the radio and receiver, as they are tied together and that radio will not bind to other receivers.
The servo is a 3 wire servo (double check that) so it will work with other radios/ESC's
The battery will power a brushless system. I am not sure on the proper "low voltage cutoff" level for Li-ion batteries. Most all RC speed controls that have low voltage cutoff are set for Lipo batteries (usually somewhere between 3.0 and 3.3v/cell) It is possible that that cutoff may be too low for Li-ion batteries. Or it may be fine, you would have to research what is a proper cutoff voltage. Im sure there is some info, as there are those in the RC world that use Li-ion packs.

If the stock 370 motor gives you trouble (I know mine wore out fast due to dirt/sand getting inside) then it might be better to consider another brand motor. There are some venom 370 motors and the losi 370 motor. They are not too expensive, and they might last longer than the stock one. Might even give a slight performance increase too.

I mention this option because that truck may not hold up very well to a brushless system. The diff gears, spur gear and even drive shafts might start breaking if you increase the power.