This paper proposes an approach for maximising the linearity of a multi-bit digital power amplifier (DPA) by optimising the discrete levels of its parallel amplification power. By exploiting the statistical distribution of the orthogonal frequency division multiplexing (OFDM) signal, the non-linear errors can be minimised with a careful selection of these discrete power levels. The minimisation is solved based on either minimising a distortion function or through a global searching algorithm. Compared to uniform quantisation, our proposed minimisation approaches attain an optimal quantisation which improves the error vector magnitude (EVM) by 3 dB on average. The resultant optimal power levels can be applied in the design of novel high linear DPAs.