Did you read that link? You drop the FastLed library and use another one that uses the DMA function of the processor.
DMA stands for direct memory access where data is transferred directly from one place in the memory to another, without using any CPU time so you can do all you want with one processor.
I am not sure your are ready for such advanced concepts. Both my and the link methods need some skill and understanding I am afraid is not a complete beginners project.